SEXUAL DIMORPHISM IN NEMERTEANS. 45 



of littoral species, although they lie far anterior to the intestine 

 proper. Yet in this and related forms the intestinal diverticula 

 extend far forward, even in front of the brain in many cases. It 

 is evident that in their embryonic development these diverticula 

 actually grow anteriorly from their primitive lateral positions, 

 and it is quite conceivable that they carry with^them the rudi- 

 ments of the gonads and that only those gonads which are thus 

 carried forward develop into spermaries. Serious objections to 

 this hypothesis are, first, that the number of spermaries bears no 

 relation to the number of cephalic diverticula present in the 

 adult, and, second, even with this hypothesis a certain amount of 

 independent migration would be necessary to give the spermaries 

 their definite localization. 



The number of intestinal diverticula in this species is commonly 

 between thirty and fifty and the ovaries retain their primitive 

 positions between them (Fig. 4). One of the females available 

 for study, although of large size, had the ovaries in a very 

 early stage of development. In this case these organs alternated 

 regularly with the intestinal diverticula except toward the pos- 

 terior end of the body. But in the specimens with mature 

 ovaries the number was much less than that of the diverticula, 

 ranging from about fifteen to twenty pairs (Fig. 4). ' Evidently 

 some of the original ovaries have failed to develop or have been 

 absorbed by the body tissues. 



This process if carried still farther would result in a condition 

 similar to that which Burger ('06) found in a related species, 

 P. woodworlhi, in which there are only seven or eight pairs of 

 ovaries. Burger also found in a specimen which he erroneously 

 identifies as P. agassizii "numerous" very young ovaries which 

 alternate regularly with the diverticula in the middle portions 

 of the body, although he does not state the precise number. 

 Brinkmann ('16) studied a single female of P. vanhoffeni which 

 had just discharged the eggs from fourteen pairs of ovaries. 



The conditions in the females of all these species are thus 

 quite in harmony with the account given above for P. agassizii, 

 but only in the latter species has the male been discovered. 



2. Balcenanemertes. Burger ('09) describes from a single speci- 

 men a new genus which in his opinion forms a connecting link 



