526 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. XXVIII. 



At first the} T are very small, simply nucleated cells, transversely 

 oblong, and not quite filling the lumen of the narrow portion of the 

 duct (c, fig. 32). As they pass backward they increase in size and 

 gradually acquire a vitelline membrane somewhere 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 

 increasing in diameter, the cells fuse somewhat and appear as a con- 

 tinuous granular mass in which it is practicall} T impossible to distinguish 

 either cell walls or nucleus (g, fig. 32). Ver} 7 quickly, however, this 



mass begins to differentiate 

 again into separate eggs, in 

 each of which the } 7 olk or 

 nutrient material separates 

 from the white or animal 

 material. The eggs are now 

 flattened together more and 

 more strong!} 7 through the 

 pressure generated by their 

 growth and finally become 

 biscuit-shaped as they ap- 

 proach the external open- 

 ing (b). This posterior por- 

 tion of the oviduct is called 

 by 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 they pass through. 

 During the passage each 

 egg is fertilized by sperm 

 from the sperm receptacles, 

 whose duct opens into the 



Fig. 32.— Genital segment of Caligus rapax. b, eggs 



FULLY FORMED AND READY TO BE PUSHED OUT INTO THE 

 EGG CASES; C, EGGS AS SIMPLE NUCLEATED CELLS "WITH- 

 OUT ANY YOLK; e, EGGS AFTER EXTRUSION AND FERTILI- 

 ZATION; g, EGGS FUSED TOGETHER JUST AFTER ACQUIRING 

 THE YOLK PARTICLES. 



oviduct very close to the external opening. 



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

 nomenclature of Rathke and Claus might well be called the os uteri 

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

 very close to the posterior 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, corresponding!} 7 diminished in 



