a, Arrow from proboscis-cavity (pc) passing to left of pericardium (per) and out through proboscis pore-canal.
b1, arrow from central canal of neurochord (cnc) passed out through anterior neuropore.
b2, ditto; through posterior neuropore.
c, arrow intended to pass from 1st gill-pouch through collar pore-canal into collar-coelom (cc).
cts, posterior limit of collar.
dv, dorsal vessel passing into central sinus (bs).
ev, efferent vessel passing into ventral vessel (vv).
epr, epiphysial tubes.
st, stomochord.
vs, ventral septum of proboscis.
sk, body of nuchal skeleton.
m, mouth.
th, throat.
tb, tongue-bars.
tc, trunk coelom.
Reproductive System.—The sexes are separate, and when mature are sometimes distinguished by small differences of colour in the genital region. Both male and female gonads consist of more or less lobulated hollow sacs connected with the epidermis by short ducts. In their disposition they are either uniserial, biserial or multiserial. They occur in the branchial region, and also extend to a variable distance behind it. In exceptional cases they are either confined to the branchial region or excluded from it. When they are arranged in uniserial or biserial rows the genital ducts open into or near the branchial grooves in the region of the pharynx and in a corresponding position in the post-branchial region. An important feature is the occurrence in some species (Ptychoderidae) of paired longitudinal pleural or lateral folds of the body which are mobile, and can be approximated at their free edges so as to close in the dorsal surface, embracing both the median dorsal nerve-tract and the branchial grooves with the gill-pores, so as to form a temporary peri-branchial and medullary tube, open behind where the folds cease. On the other hand, they can be spread out horizontally so as to expose their own upper side as well as the dorsal surface of the body (fig. 1). These folds are called the genital pleurae because they contain the bulk of the gonads. Correlated with the presence of the genital pleurae there is a pair of vascular folds of the basement membrane proceeding from the dorsal wall of the gut in the post-branchial portion of the branchio-genital region, and from the dorsal angles made by the pleural folds with the body-wall in the pharyngeal region; they pass, in their most fully developed condition, to the free border of the genital pleurae. These vascular membranes are called the lateral septa. Since there are many species which do not possess these genital pleurae, the question arises as to whether their presence or their absence is the more primitive condition. Without attempting to answer this question categorically, it may be pointed out that within the limits of the family (Ptychoderidae) which is especially characterized by their presence there are some species in
which the genital pleurae are quite obsolete, and yet lateral septa occur (e.g. Ptychodera ruficollis), seeming to indicate that the pleural folds have in such cases been secondarily suppressed.
Development.—The development of Balanoglossus takes place according to two different schemes, known as direct and indirect, correlated with the occurrence in the group of two kinds of ova, large and small. Direct development, in which the adult form is achieved without striking metamorphosis by a gradual succession of stages, seems to be confined to the family Balanoglossidae. The remaining two families of Enteropneusta, Ptychoderidae and Spengelidae, contain species of which probably all pursue an indirect course of development, culminating in a metamorphosis by which the adult form is attained. In these cases the larva, called Tornaria, is pelagic and transparent, and possesses a complicated ciliated seam, the longitudinal ciliated band, often drawn out into convoluted bays and lappets. In addition to this ciliated band the form of the Tornaria is quite characteristic and unlike the adult. The Tornaria larva offers a certain similarity to larvae of Echinoderms (sea-urchins, star-fishes, and sea-cucumbers), and when first discovered was so described. It is within the bounds of possibility that Tornaria actually does indicate a remote affinity on the part of the Enteropneusta to the Echinoderms, not only on account of its external form, but also by reason of the possession of a dorsal water-pore communicating with the anterior body-cavity. In the direct development Bateson showed that the three divisions of the coelom arise as pouches constricted off from the archenteron or primitive gut, thus resembling the development of the mesoblastic somites of Amphioxus. It would appear that while the direct development throws light upon the special plan of organization of the Enteropneusta, the indirect development affords a clue to their possible derivation. However this may be, it is sufficiently remarkable that a small and circumscribed group like the Enteropneusta, which presents such a comparatively uniform plan of composition and of external form, should follow two such diverse methods of development.
Distribution.—Some thirty species of Balanoglossus are known, distributed among all the principal marine provinces from Greenland to New Zealand. The species which occurs in the English Channel is Ptychodera sarniensis. The Ptychoderidae and Spengelidae are predominantly tropical and subtropical, while the Balanoglossidae are predominantly arctic and temperate in their distribution. One of the most singular facts concerning the geographical distribution of Enteropneusta has recently been brought to light by Benham, who found a species of Balanoglossus, sensu stricto, on the coast of New Zealand hardly distinguishable from one occurring off Japan. Finally, Glandiceps abyssicola (Spengelidae) was dredged during the "Challenger" expedition in the Atlantic Ocean off the coast of Africa at a depth of 2500 fathoms.
Authorities.—W. Bateson, "Memoirs on the Direct Development of Balanoglossus," Quart. Journ. Micr. Sci. (vols. xxiv.-xxvi., 1884-1886); W. B. Benham, "Balanoglossus otagoensis, n. sp," Q. J. M. S. (vol. xlii. p. 497, 1899); Yves Delage and Éd. Hérouard, Traité de zoologie concrète (t. viii.), "Les Procordés" (1898); S. F. Harmer, "Note on the Name Balanoglossus," Proc. Camb. Phil. Soc. (x. p. 190, 1900); T. H. Morgan, "Memoirs on the Indirect Development of Balanoglossus," Journ. Morph. (vol. v., 1891, and vol. ix., 1894); W. E. Ritter, "Harrimania maculosa, a new Genus and Species of Enteropneusta from Alaska," Papers from the Harriman Alaska Exhibition (ii.), Proc. Washington Ac. (ii. p. 111, 1900); J. W. Spengel, "Die Enteropneusten," Eighteenth Monograph on the Fauna und Flora des Golfes von Neapel (1893); A. Willey, "Enteropneusta from the South Pacific, with Notes on the West Indian Species," Zool. Results (Willey), part iii., 1899; see also Q. J. M. S. (vol. xlii. p. 223, 1899); J. P. Hill, "The Enteropneusta of Funafuti," Mem. Austral. Mus. (iii., 1897-1898); M. Caullery and F. Mesnil, "Balanoglossus Kochleri, n. sp. English Channel," C. R. Soc. Biol. lii. p. 256 (1900).
(A. W.*)
BALARD, ANTOINE JERÔME (1802-1876), French chemist, was born at Montpellier on the 30th of September 1802. He started as an apothecary, but taking up teaching he acted as chemical assistant at the faculty of sciences of his native town, and then became professor of chemistry at the royal college and school of pharmacy and at the faculty of sciences. In 1826 he discovered in sea-water a substance which he recognized as a previously unknown element and named bromine. The reputation brought him by this achievement secured his election as successor to L. J. Thénard in the chair of chemistry at the faculty of sciences in Paris, and in 1851 he was appointed professor of chemistry at the Collège de France, where he had M. P. E. Berthelot first as pupil, then as assistant and finally as colleague. He died in Paris on the 30th of April 1876. While the discovery of bromine and the preparation of many of its compounds was his most conspicuous piece of work, Balard was an industrious chemist on both the pure and applied sides. In his researches on the bleaching compounds of chlorine he was the first to advance the view that bleaching-powder is a double compound of calcium chloride and hypochlorite; and he devoted much time to the problem of economically obtaining soda and potash from sea-water, though here his efforts were nullified by the discovery of the much richer sources of supply afforded by the Stassfurt deposits. In organic chemistry he published papers on the decomposition of ammonium oxalate, with formation of oxamic acid, on amyl alcohol, on the cyanides, and on the difference in constitution between nitric and sulphuric ether.
BALA SERIES, in geology, a series of dark slates and sandstones with beds of limestone which occurs in the neighbourhood of Bala, Merionethshire, North Wales. It was first described by A. Sedgwick, who considered it to be the upper part of his Cambrian System. The series is now placed at the top of the Ordovician System, above the Llandeilo beds. The Bala limestone is from 20 to 40 ft. thick, and is recognizable over most of North Wales; it is regarded as the equivalent of the Coniston limestone of the Lake District. The series in the type area consists of the Hirnant limestone, a thin inconstant bed, which is separated by 1400 ft. of slates from the Bala limestone, below this are more slates and volcanic rocks. The latter are represented by large contemporaneous deposits of tuff and felsitic lava which in the Snowdon District are several thousand feet thick. In South Wales the Bala Series contains the following beds in descending order:—the Trinucleus seticornis beds (Slade beds, Redhill shales and Sholeshook limestone), the Robeston Wathen beds, and the Dicranograptus shales. The typical graptolites are, in the upper part, Dicellograptus anceps and D. complanatus; in the lower part, Pleurograptus linearis and Dicranograptus Clingani. In Shropshire this series is represented by the Caradoc and Chirbury Series; in southern Scotland by the Hartfell and Ardmillan Series, and by similar rocks in Ireland. See Caradoc Series and Ordovician System.