No. 2.1 STOLONIZATION IN AUTOLYTUS VARIANS. -iix 



intrinsic part of the anal segment, this segment, as compared 

 with the other segments of the stolon, is so embryonic in char- 

 acter, and its posterior outlines so poorly defined, that at the time 

 of separation it has hardly attained the value of a distinct seg- 

 ment. The appearance of this region in longitudinal section at 

 once seems to suggest that the separation of the stolon does not 

 take place in the tissues forming a part of a true segment, but 

 rather in a mass of embryonic tissue, which in the development 

 of the head and buccal segment has been formed as an embry- 

 onic union of these and the anal segments, and constitutes a nar- 

 row undefined band of embryonic tissue anterior and posterior to 

 which similar embryonic cells are undergoing differentiation, 

 while at the same time the embryonic cells of this region are be- 

 ginning to degenerate. The embryonic regions of the buccal 

 and anal segments are hence continuous, and it is in the midst 

 of this undifferentiated region that the degeneration of the cells 

 appears and separation takes place. 



Position of the Chain. 



The position of the chain of stolons in Autolytus varians, as 

 I have already indicated, is not constant, but varies consider- 

 ably in different specimens. Like the chain-forming species, 

 A. ehbiensis and A. edwarsi, described by de St.-Joseph, the 

 region of stolonization in this species has a similar range, 

 although the position of the chain is never as far forward as 

 in the species described by this author. In a hundred speci- 

 mens examined, the greater number of chains were found to 

 be attached to segments between the 3 2d and 38th setigerous 

 segments. A small number bore the chain posterior to seg- 

 ments 45-48, and a still smaller number bore the chain of 

 stolons as far forward as segments 23-28. A few specimens 

 were found, in which the chain was placed as far forward as 

 the 19th and 21st setigerous segments, while a few others were 

 also found, in which the chain was borne as far back as seg- 

 ments 56 and 58. The range of stolonization in this species, 

 therefore, is between setigerous segments 19-58. 



In describing the position of the chain of stolons, Malaquin 

 and de St.-Joseph appear to regard this great difference in the 



