198 PAUL S. WELCH. 



the cocoon opening. Such body diminution is said to occur 

 in certain other animals when subjected to a continued absence 

 of food. Failure to emerge by non-bifurcate individuals was 

 apparently due to abnormal proportions, this condition being 

 attained before the individual was ready to leave the cocoon. 



REARING OF BIFURCATE INDIVIDUALS. 



Attempts were made to determine whether it is possible for 

 bifurcate individuals to live and develop if assisted in escaping 

 from their cocoons. In order to insure that they had reached 

 a degree of development at least comparable with that of their 

 normal fellows which were escaping and successfully assuming 

 the free-living life, cocoons containing bifurcations were isolated 

 and bifurcate individuals allowed to remain in the cocoons until 

 most or all normal individuals had emerged. Then the former 

 were dissected out with as great care as possible and introduced 

 into a culture identical in composition and operation with the 

 one in which the normal, newly emerged worms were thriving. 

 Normal worms were used in this way as controls. Up to date 

 the writer has been unable to rear a single bifurcation, although 

 the controls were easily maintained. The reasons for this 

 failure are not understood at present. 



ABSENCE IN NATURAL CONDITIONS. 



The almost complete, if not wholly complete, absence of 

 bifurcate individuals of Tiibifex tubifex in nature is shown by 

 the fact that in an examination of over 1,000 worms representing 

 various degrees of maturity and immaturity and collected both 

 from cultures and from native environments not a bifid form 

 was found. The literature seems to contain only one record 

 (Abel, 1902) of a bifid tubificid found in nature, but since similar 

 results have been produced artificially in post-embryonic stages, 

 there is no certainty that Abel's record has any significance in 

 this connection since it might have resulted from an accidental 

 injury. Evidently the cocoon constitutes a very efficient device 

 which automatically eliminates the vast majority of abnor- 

 malities. 



