The Anatomy of Ojnsthopatiis cinctipes. 81 



say whether it is. normally present or merely caused by defective 

 sectioning. From appearances the latter seems to be the most 

 probable supposition. 



There can be no doubt that this loop is a much simplified form of 

 the receptaculum seminis found in Perijjatus, Perijoatoides and 

 Paraperipatus, in all of which the lobes are very much larger, owing 

 to the considerable dilatation of the convex portion of the loop. In 

 Peripatus (Gaffron, 1885) and Paraperipatus (Willey, 1898) the short 

 direct communication between the portions of the oviduct on each 

 side of the receptaculum is normal. 



Gaffron has shown that this more complicated receptaculum owes 

 its origin to a folding up of the oviduct, exactly resembling that 

 which is the normal condition in OpistJiopatus (see also Willey, 1898, 

 text-fig. on p. 11). 



In Opistliopatas the portion {in) of the duct which lies between the 

 receptaculum and the ovary has very thick walls and a small lumen, 

 differing in these respects from the part {od) on the other side of the 

 receptaculum, where the walls are much thinner and the lumen much 

 larger. Willey noticed a similar difference in the corresponding 

 portions of the oviduct in Paraperipatus and he proposes the term 

 ■infiindihulum as a special name for the part lying between the 

 receptaculum and the ovary (p. 10). 



The principal interest in the simplified receptaculum seminis of 

 0. cinctipes lies in the circumstance that it supplies an intermediate 

 form between the more complicated organ of Peripatus, &c., and the 

 condition in Peripiatopsis, in which no receptaculum seminis occurs 

 at all. For by slightly decreasing the size of the loop and then 

 straightening out the latter, the receptaculum in Opisthopatus would 

 vanish at once. 



The embryos. — In the early segmentation stages the ova appear to 

 be finely and densely vacuolated throughout and are provided with 

 large nuclei. They are of comparatively small size, measuring less 

 than -1 mm. in lesser diameter, or apparently only about half that of 

 similar ova in P. halfouri. I have, however, only seen the ova in 

 sections, and cannot give the accurate dimensions. 



I failed to observe any direct connection in any stage between the 

 embryos and the uterine wall similar to that found in Peripatus. On 

 the contrary, the former always appeared to lie free in its uterine 

 chamber, although in contact with the walls of the latter at various 

 places, and, as in Peripatopsis, part of the dorsal ectoderm is much 

 thickened in certain stages. These stages in Peripiatopsis have been 

 described by Sedgwick, who considers that the thickened ectoderm 



