The entomologist Latreille also tackled the problem of the homologies of the segments in the different classes of Arthropods (Cuvier, loc. cit., p. cclxxii.). He thought he could find fifteen segments in all Arthropods. He made the retrograde step of likening the head of insects to a single segment. But some of his homologies showed morphological insight, e.g., his comparison of the "first jaws" of Arachnids to antennæ, because they were placed above the upper lip. It was he who first pointed out the resemblance of the leaf-like gills of Ephemerid larvæ to wings, and suggested that wings were "a sort of tracheal feet."
He made also a rather hazy and speculative contribution on Okenian lines to the problem of the relation of Arthropods to Vertebrates, likening the carapace of Crustacea to an enormously developed hyoid, the appendages of the tail to the ventral and anal fins of fish. The masticatory organs of Arthropods were jaws disjointed at their symphysis; antennæ, nostrils turned outside in.
Dugès also made a comparison of Articulates with Vertebrates.[139] He did not accept Geoffroy's vertebral theory of the Arthropod skeleton, though he admitted that in Arthropods the dorsal surface was turned towards the ground, basing this assumption on the position of the nervous system, and also, curiously enough, on the inverted position of the embryo on the lower surface of the yolk. He considered that the mandibles and first maxillæ of Arthropods were the homologues of the upper and lower jaws of Vertebrates, adducing as confirmatory evidence the fact that in snakes the rami are separate. The labium was the equivalent of the hyoid, the labial palps and maxillipedes the equivalent of the "hyoid" elements which form the branchial arches.
But Dugès' main contribution to morphological method was his conception of the living organism as a colony of lesser units, which were themselves real "organisms." "By organism the author means a complex of organs which taken together suffice to constitute, ideally or actually, a complete animal. An 'organism' is, as it were, an elementary or simple animal; several organisms combined form a complex animal" (p. 255). Dugès hit upon this principle, which was first suggested to him by A. Moquin-Tandon's work on the leech (1827), as a great aid in demonstrating the unity of plan and composition throughout the animal kingdom.[140] According to his view there are three main types of animals—(1) Biserials, including bilaterally symmetrical animals, composed of two parallel series of "organisms"; (2) Radiates, composed of "organisms" arranged like the spokes of a wheel; and (3) Raceme-animals, in which the separate "organisms" were disposed more or less irregularly, in bunches (p. 257). The unitary "organism" is supposed to be the same in all, only the arrangement differing. Dugès of course admitted that the centralisation of the complete organism became greater the higher it stood in the scale, and that this held good also in individual development. The appendages of Articulates and Vertebrates were thought of as the members of as many separate organisms. He went so far as to suggest that the fingers of a man's hand were the free extremities of as many thoracic members.
Dugès' conception of the organism has often been revived since in a saner form, e.g., by E. Perrier, and it has a certain validity. It has much affinity with the similar conceptions of Goethe and the German transcendentalists.
[130] Mem. Acad. Sci., iv., pp. cclxxxiv.-ccci., 1824.
[131] Ann. Sci. Nat., xi., xii., 1827; xvi., 1829; xxi., 1830.
[132] See Rádl, loc. cit., i., pp. 225-6.
[133] Ann. Sci. nat. (2), ii., p. 248, 1834.
[134] Ann. Sci. nat., iii., pp. 377-80, 1824.