_Permanent renal organ._ According to the most recent observer (Rabl, No. 268), whose statements are supported by the sections figured, the permanent renal organ in Gasteropods is developed from a mass of mesoblast cells close to the end of the intestine. This is first carried somewhat to the left side, and then becomes elongated and hollow, and attaches itself to the epiblast on the left side of the anus (fig. 108, _r_). After the formation of the heart the inner end opens into the pericardium and becomes ciliated, the median part becomes glandular and concrements appear in its lining cells, and the terminal part forms the duct. Previous observers have usually derived this organ from the epiblast; according to Rabl this is owing to their having studied too late a stage in the development. In Cephalopoda the excretory sacks or organ of Bojanus are apparently differentiations of the mesoblast[115]. At an early stage part of their walls envelops the branchial veins. From this part of the wall the true glandular section of the organ would seem to be formed. The epithelium forming the inner wall of each sack is at an early age very columnar. [115] I conclude this from Bobretzky's figures. The development of the organ of Bojanus in Lamellibranchiata has been studied by Lankester. He finds that it develops as a paired invagination of the epiblast immediately ventral to the anus. Generative glands. The generative glands in Mollusca would appear to be usually developed in the post-larval period, but our knowledge on this subject is extremely scanty. In Pteropods Fol believes that he has proved that the hermaphrodite gland originates from two independent formations, one (the testicular) epiblastic in origin, and the other (the ovarian) hypoblastic. These views of Fol do not appear to me nearly sufficiently substantiated to be at present accepted. The generative glands in Cephalopoda appear to be simple differentiations of the mesoblast. They are at first very closely connected with the aortic heart (fig. 127, _kd_), but soon become completely separated from it. Alimentary tract. The formation of the archenteron, and the relation of its opening to the permanent mouth and anus, has already been described and needs no further elucidation. It will be convenient to treat the subject of this section under three headings for each group--viz. (1) the mesenteron, (2) the stomodæum, and (3) the proctodæum.