112 S- SOTO. 



was also a rather thick layer of granular substance on its wall (PI. IV, 

 fig. 8), wliich I believe to be the secretion of the shell-glands. In 

 OnclwcoUjle the ootyp presents in cross-section a very peculiar ap- 

 pearance. Its cavity looks stellate, caused by the fact that the 

 cells that constitute its epithelium have assumed a laterally 

 flattened conical form and are arranged in close series in parallel 

 longitudinal linos, so that the wall is, so to speak, furnished with 

 pilasters projecting into the cavity of the ootyp (PI. XVI, fig. 4). 

 That these pilasters are composed of cells is clear from the fact that 

 here and there in cross-sections nuclei are observed near the outermost 

 end of the sections of the pilasters ; the comparative fewness of the 

 nuclei being accounted for by supposing that the cells have been much 

 elongated parallel to the length of the ootyp. The individual cells 

 are completely fused with each other, and no boundary line can be 

 observed ; the furrows between the pilasters, however, probably mark 

 the boundaries between the longitudinal series of cells. The wall of 

 the ootyp is separated from the mesenchyma by a distinct basement 

 membrane ; but there is no membrane on its inner surface (PI. XVI, 

 fig. 4), In Tristomum the wall of the ootyp consists of a sort of 

 syncytium in which nuclei are sparsely dispersed, and which is 

 separated from the mesenchyma by a basement membrane. The 

 syncytium itself stains well, is very finely granular, and has no 

 membrane on its- free surface (Pi. XXII, fig. 3). The nuclei seems 

 sometimes to be very regularly distributed : for instance, in Tristomum 

 sinuatmn I have observed in a median longitudinal section of the 

 ootyp four nuclei arranged in pairs in the central portion and two 

 others also arranged in a pair near the oviduct end (PI. XXII, 

 fig. 8) ; they were all vesicular, stained rather weakly, and contained 

 each a single, deeply staining nucleolus. In CalicotyU and Mmiocotijlc 

 the wall of the ootyp consists of a true epithelium resting on a basement 



