ASEXUAL CYCLE OF PI.ANARIA VELATA. 



197 



insufficient the worm fails to fragment. In such cases parts of 

 the body may become greatly elongated and a string of connected 

 masses may arise. Figure 6 shows such a case. 

 In the posterior region four distinct masses can 

 be distinguished. These are connected by slen- 

 der bands which are merely portions of the 

 body greatly reduced in diameter. These four 

 masses are connected with the anterior portion 

 of the body by a long slender band resulting 

 from the stretching of the middle region in 

 consequence of the attempts of the head region 

 to pull away from the attached posterior parts. 

 These greatly elongated regions of the body 

 consist of little more than the body-wall and 

 muscles; the alimentary tract and the paren- 

 chyma may be almost or entirely squeezed out 

 of them. This animal finally became surrounded 

 by a cyst in the form shown in the figure, but 

 later the connecting strands apparently atro- 

 phied, the pieces became entirely separate and 

 each produced a whole worm. 



VI. THE DEVELOPMENT OF THE WHOLE ANIMAL WITHIN THE 



CYST. 



The development of the animal from the encysted piece, 

 whether isolated artificially by section or by the natural process 

 of fragmentation, is similar in all respects to the regulatory de- 

 velopment of pieces which reproduce new wholes without en- 

 cystment. This is show T n to be the case by the removal of the 

 cysts from pieces at various stages of the process. In all cases 

 the pieces are simply undergoing regulation. The process with- 

 in the cyst may, however, be slower than in the unencysted piece, 

 probably because the supply of oxygen within the cysts is less 

 than in the water. 



The natural method of asexual reproduction in this species 

 does not then differ essentially in any way from the process of 

 experimental reproduction. The process of fragmentation gives 



