The coelomic cavity, known as the premandibular cavity, divides into a dorsal and a ventral part; the walls of the dorsal part give origin to the somatic muscles belonging to the oculomotor nerve, while the walls of the ventral part on each side form the connecting stalk between the two cavities, and give origin to the glandular hypophysis. Now, as already pointed out, the premandibular cavity is homologous with the 2nd prosomatic coelomic cavity of Limulus, and this 2nd prosomatic coelomic cavity divides, according to Kishinouye, into a dorsal and a ventral part; and, further, the walls of this ventral part form the coxal gland. Both in the vertebrate, then, and in Limulus, we find a marked glandular tissue in a corresponding position, and the conclusion is forced upon us that the glandular hypophysis was originally the coxal gland of the invertebrate ancestor. As in all other cases already considered, when the facts of topographical anatomy, of morphology and of embryology, all combine to the same conclusion as to the derivation of the vertebrate organ from that of the invertebrate, then there must be also a structural similarity between the two. What, then, is the nature of the coxal gland in the scorpions and Limulus? Lankester's paper gives us full information on this point as far as the scorpion and Limulus are concerned, and he shows that the coxal gland of Limulus differs markedly from that of Scorpio in the size of the cells and in the {321}arrangement of the tubes. In Fig. 126, A, I give a picture of a piece of the coxal gland of Limulus taken from Lankester's paper. Turning now to the vertebrate, Bela Haller's paper gives us a number of pictures of the glandular hypophysis from various vertebrates, and he especially points out the tubular nature of the gland and its solidification in the course of development in some cases. In Fig. 126, B, I give his picture of the gland in Ammocoetes. The striking likeness between Haller's picture and Lankester's picture is apparent on the face of it, and shows clearly that the histological structure of the glands in the two cases confirms the deductions drawn from their anatomical and morphological positions. [Illustration: FIG. 126.--A, SECTION OF COXAL GLAND OF LIMULUS (from LANKESTER); B, SECTION OF PITUITARY BODY OF AMMOCOETES (from BELA HALLER). _n.a._, termination of nasal passage.] The sequence of events which gave rise to the pituitary body of the vertebrate was in all probability somewhat as follows:--