ON THE DEVELOPMENT OF PARASITIC COPEPODS. 49 



become elongate curved bodies that remain for a long time. 

 The spermatozoa fill the center of the vas deferens and lie parallel 

 to one another. In the spermatophores they extend radially 

 from the nutritive walls. In spermatophores that have been 

 attached to the female a long time, the nutritive material has 

 disappeared, leaving a mass resembling evacuated cell walls. 



The same description of the spermatogenesis holds in general 

 for Pandams siiniatns, though there are many minor differences. 

 As regards the behavior of these nutritive bodies I have observed 

 one similar instance, in Peripaius, but in Peripatns the nutritive 

 bodies are nuclei of degenerating cells. In these copepods the 

 nutritive body appears to form in or in close relation to the 

 nucleus, but too little is known both of the nutritive bodies in 

 Peripatns and copepods to suppose them genetically related. 



VI. POLARITY OF THE EGG. 



The fertilized egg and embryo in all cases in which the egg 

 string extends straight behind the animal and contains a single 

 linear series of eggs, is definitely oriented in relation to the 

 mother. The animal pole of the egg is posterior and the first 

 protoplasmic cell and resulting head end of the embryo is latero- 

 ventral. The chief axis of the egg is manifested in the ovary in 

 the flattening of the egg (being the shortest axis). In any stage 

 in which the primary oocyte is considerably thicker than the 

 diameter of the nucleus, the latter lies nearer the animal pole. 

 The head end of the embryo coincides with the region in which 

 the first protoplasmic cell is formed, and this is probably deter- 

 mined by the point of entrance of the sperm. The seminal 

 receptical opens into the oviduct by a small orifice which would 

 lead sperm to the egg at or near the position of the future head 

 of the embryo. Cases of rotation of the long axis of the embryo, 

 which sometimes occur, might be due to the spermatozoon getting 

 around the egg before entering. 



The first polar body is extruded in a slightly eccentric position 

 on that flat side of the egg directed toward the free end of the 

 egg string. Thus the chief axis of the egg does not exactly 

 coincide with the shortest axis, but is a little inclined toward the 

 anterior end, yet not enough to cause the first polar body to lie 



