142 MUNSON. [Vol. XV. 



in the chapter on natural history, this period may of course be 

 greatly extended. It is seen from those observations, also, 

 that after the period of sexual maturity, which may be reckoned 

 from the first discharge of eggs into the ovarian tubes, the 

 phenomena of moulting, if not entirely suspended, become at 

 least less frequent. It may be supposed that from the period 

 of sexual maturity the animal does not increase so rapidly in 

 size. That it does increase in size after the period of sexual 

 maturity seems probable from the fact that females that were 

 observed ovipositing differed considerably in size. 



The original germ cells (oogonia), up to the time when the 

 embryo measures five inches, including the tail, multiply by an 

 equal division. At this stage they number about eight in cross 

 section. This marks the end of t\\Q period of tnultiplication. 



At about the sixth-inch stage of the animal a new period in 

 their history begins — the period of growth. This is immedi- 

 ately preceded by a multiplication process differing from the 

 former in that the products of division are dissimilar. The 

 karyokinetic processes by which this takes place have previ- 

 ously been described. The result of this process is the forma- 

 tion of a group of cells, one of which becomes the growing 

 oocyte, while the others belonging to the same group become 

 temporarily the follicle which ultimately forms the permanent 

 epithelium of the ovarian tube. In this way the original germ 

 cell has acquired a new environment, inasmuch as it is hence- 

 forth destined to be removed farther from the lumen of the 

 ovarian tube, and is guarded by its daughter cells, which, as 

 follicle and epithelial cells, serve to nourish and protect it. 



This transformation of the original oogonia into the pro- 

 tected, specially nourished, and consequently growing odcyte 

 does not take place simultaneously in all the original oogonia, 

 but it is first accomplished in that one farthest removed from 

 the point of attachment of the ovarian tube (PI. XIV, Fig. 

 41). From now on, this first-formed oocyte continues to 

 grow as the animal grows, and is the first to arrive at that 

 stage of maturity which marks its discharge into the ovarian 

 tube when the period of sexual maturity of the animal is 

 reached. 



