390 E. RAY LANKESTElli 



"As yet the alimentary tract traverses the body almost in a 

 straight line (i) ; but, now as the body becomes more 

 elongated and cylindrical, it begins to bend on itself, and the 

 anus takes up a position forward on the right-hand side. At 

 the same time the mantle-margin grows greatly, and the 

 hinder part of the body rises up in a dome-like fashion. On 

 it one can now observe the small cap-like shell {g), and in 

 the body a to-and-fro circulation, such as is seen in a much 

 more marked manner in the land Pulmonata. 



" The foot forms now a prominent bilobed process, and above 

 it near the mouth, which also begins to push forward in a 

 snout-like fashion (k), the tentacles are seen, and at their 

 bases the eyes. The mantle ridge arches now more and more 

 widely forward and raises itself up, so that we can now 

 clearly distinguish a lung-chamber, in which ciliary move- 

 ment is observed ; also the heart is recognised by its 

 contractions in the middle line behind the mantle-ridge. 



" In the neck region the first rudiment of the nervous 

 system is now seen (l), whilst the foot grows considerably, 

 as also the shell-bearing hind-body. 



" In the pharynx the commencement of the odontophor is 

 seen, and in the further developed lung-chamber the kidney. 

 Upon the eye-pigment a lens is now clearly seen, and now, 

 at last, according to Lereboullet, the otocysts make their 

 appearance, which in most snails appear in a much earlier 

 stage. 



" At first the otocysts are empty, but gradually the otoliths 

 are secreted, and cilia appear on the walls of the sacs. 



" The embryo is now so large that it fills up the egg-shell, 

 and soon breaks it and creeps out. The rate of development 

 varies much, according to temperature, but lasts at least 

 twenty days, and may take double that time." 



In reference to the passages lettered in the preceding quo- 

 tation, the observations recorded in this paper lead to the 

 following corrections : 



A. The velum is not wanting in the freshwater Pulmonata ; 

 in its earlier annular and in its later heart-shaped form it is 

 well developed, and becomes the subtentacular lobes of the 

 adult Lymnseus. 



B. The origin of the four smaller cells from a single 

 pellucid cell, coexisting with four larger cells, is not satisfac- 

 torily demonstrated, such a single pellucid cell being possibly 

 only a Richtungsblaschen. 



c. Nor is the enclosure of the smaller by the larger 

 cleavage-spheres clearly made out, though possible enough. 

 D. The in-sinking and its orifice are not the alimentary 



