526 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. xxvni. 



At Hr.st they are \('ry small, siiii[)ly miclcatod cells, transversely 

 ol)long", and not ([uit(^ tillinu- the lumen of the narrow portion of the 

 duct (c, tio-. 82). As they pass backward they increase in size and 

 gradually acquire a \ itelline membrane somewdiere in the posterior 

 thoracic area. The cell contents also become finely granular with yolk 

 particles, so that on emerging into the genital segment and suddenly 

 increasijig in diameter, the cells fuse somewhat and ai)pear as a con- 

 tinuous graiuilar mass in which it is practically impossible to distinguish 

 either cell walls or nucleus (g, tig. 32). Ver}^ quickly, however, this 



mass begins to differentiate 

 again into separate eggs, in 

 each of which the yolk or 

 mitrient material separates 

 from the white or animal 

 material. The eggs are now 

 flattened together more and 

 more strongly through the 

 pressure generated by their 

 growtli and linally become 

 biscuit-shaped as the}" ap- 

 proach the external open- 

 ing (b). This posterior por- 

 tion of the oviduct is called 

 ])y Rathke the uterus (u, fig. 

 31), and Claus remarks that 

 the name is well applied, 

 since the eggs remain here 

 a long time. The oviduct 

 is considerably narrowed 

 just before reaching the 

 external opening, and the 

 eggs must be altered in 

 shape as the}^ pass through. 

 During the passage each 

 egg is fertilized by sperm 

 from the sperm receptacles, 

 whose duct opens into the 

 oviduct ver}" close to the external opening. 



This opening of the oviduct to the exterior, which to follow out the 

 nomenclature of Rathk(Mui<l Claus might well l)e called the os uteii 

 (o. u., fig. 31) is situated on the ventral surface of the genital segment 

 very close to the ])osterior end, and usually just above the rudimen- 

 tary fifth legs. 



On emerging to the exterior the eggs suddenly widen to nearly 

 twice their former diameter, and are correspondingly diminished in 



Fi(i. 32.— Genital segment of Caligus r.\pax. li. eggs 



KULLY FORMED AND READY TO BE PUSHED OUT INTO THK 

 EGG cases; C, eggs as simple NUCLEATED CELLS WITH- 

 OUT ANY yolk; t>, EGGS AFTER EXTRUSION AND FERTILI- 

 ZATION; g, EGGS FUSED TOGETHER .lU.ST AFTER ACQUIRIN(; 

 THE YOLK PARTICLES. 



