BIFURCATION IN EMBRYOS OF TUBIFEX. 197 



since as will be shown later deep bifurcations present difficulties 

 which are practically insuperable. 



The difficulty of escape from the cocoon by a bifurcate in- 

 dividual is due to one or both of two features, namely, the 

 increased bulk of the double end thus exceeding, ordinarily, the 

 diameter of the neck passage, and the split nature of the end 

 causing the frequent situation of one branch projecting through 

 the neck and the other turned up inside the wall a situation 

 which is prohibitive of escape. Escape by working the way out 

 backward has already been mentioned but that likewise appears 

 impossible when the posterior end is deeply bifurcate. Even 

 the most striking inequality of diameter in the arms of a bifur- 

 cation observed constitutes a serious obstacle to emergence. 

 Both anterior and posterior extiemities execute searching 

 movements and instances have been found in which a worm 

 with a deep posterior bifurcation had one posterior branch 

 projected through one neck of the cocoon and the other through 

 the opposite neck. Every kind of bifurcate individual manifests 

 movements which in the normal animal would result in emergence 

 and there seems to be no doubt whatever that failure to escape 

 is due entirely to the abnormal body structure. 



VIABILITY IN COCOONS. 



Mention has already been made of the remarkable viability 

 of some of these worms in cocoons and it should be stated in 

 this connection that both bifurcate and non-bifurcate anomalies 

 exhibit this phenomenon. The writer has records of sojourns 

 within the cocoon for varying periods with ninety-eight days as 

 a maximum and while in almost every case the individual 

 untimately died without having escaped, a few of them (even 

 in the record for ninety-eight days) finally emerged. Why 

 escape could occur after so long a period is not known since the 

 cocoon undergoes no observable change, but it is conceivable 

 that such a form living for days after all the available food 

 material apparently has been exhausted might, because of the 

 continued state of inanition, become reduced somewhat in body 

 size, this reduction permitting the animal to pass out through 



