Gordius varius, Leidy, 10 to 16 cm., female, up to 30 cm. in length (Diesing).
Gordius chilensis, Blanch. (Guy). Gordius villoti, Rosa (Bercutti, Camerano); Gordius tricuspidatus, L. Def. (R. Blanchard), Gordius violaceus, Baird (Topsent), and Gordius pustulosus, Baird (Parona).
F. HIRUDINEA s. DISCOPHORA (Leech).
Fig. 348d.—The internal organs of the leech. The creature has been opened from the dorsal surface, and part of the intestine has been removed. The testicles, with vas deferens, may be seen between the blind ducts of the intestine; beyond these on either side the segmental organs. The female genital organs are in front of the most anterior pair of testicles. (After Kennel.)
The Hirudinea, which have been appropriately included amongst the Annelida, differ in many respects from the typical members of the group; their body is long and flat, it lacks the parapodia that are characteristic to all forms of Annelida; but, on the other hand, possesses a terminal posterior sucker, and in many species there is also an anterior sucker. The mouth is terminal at the anterior end, the anus lies dorsally above the posterior sucker (fig. 348D). The body is segmented, but this is less manifest in the body covering than it is in the arrangement of the internal organs; the segmentation, nevertheless, is also indicated exteriorly by the appearance of the cutaneous sensory organs which correspond to the segments. This shows what the condition of the ganglia in the abdominal ganglion chain has taught us, that the anterior and the most posterior segments are considerably abbreviated—a part of the latter taking part in the formation of the suctorial organs. In a great many species the skin is distinctly annulated, four or five of such rings, at least in the central region of the body, appearing on one segment of the body. The condition of their body cavity is another peculiarity of the Hirudinea; it is narrowed by the powerful development of the connective tissue and the muscular system into four tubular sinuses, which have the appearance of blood-vessels. There are usually one dorsal and one ventral median trunks, as well as two lateral trunks; in addition, a particular blood-vessel system exists.
The skin consists of a very thin cuticle that is cast off from time to time; it is secreted by the underlying cylindrical epithelium, which contains numerous goblet cells. The muscular system is strongly developed; it consists of long tubular fibres, which run circularly, longitudinally and in the dorso-ventral direction; the muscular system is subject to a particular expansion in the clinging organs and at the commencement of the intestine. On the whole, the alimentary canal represents a tube running straight from the mouth to the anus, which possesses a number of blind sac-like protuberances at the sides varying according to the species. The most anterior section, the pharynx, in the leeches with maxillæ carries three chitinous, semicircular plates furnished with teeth—the jaws—which serve to tear up the epidermis in order to open the blood-vessels; in the leeches with rostra a long protractile proboscis rises from the base of the elongated pharynx. Numerous salivary glands, the secretion from which possesses toxic properties, discharge into the pharynx. The œsophagus, which follows the pharynx, and to the exterior of which numerous radiary muscles are fixed, is a suctorial organ in its entire structure. The nutriment in the larger species consists of the blood of vertebrate animals, in smaller species and in the young stages the food consists of small invertebrate animals.