On the supposed Vertehration of the Tail in Âppendicalaria. 299 



kedly. Ill my preparations the reticulation of one side is altogether 

 anterior (or posterior) to that of tli(> other side. The same phenomena 

 are seen in connection with the 2''' and 9"' pairs of reticulations. If 

 the "se^'inents" in these regions were really muscle cells we should 

 have those of the opposite sides alternating with each other (see 

 Fig. 1, IM. 18). 



2) Although the "segments" of each side in the posterior part 

 of the tail of 0. dioica correspond approximately to each other , I 

 have been unable to tind the muscle cells of the same region simi- 

 larly placed in a larval form. 



.')) A careful examination of the breaks in the musculature of 

 O. dioica shows that their appearance is quite incompatible with 

 Seelkjer's explanation. Their characteristics I have already pointed 

 out, and I tind it impossible to recognise in them any evidence of a 

 ''resolution of the muscle bands into single cells". In a very young 

 0. dioica where the muscle tibres are just being formed the boundary 

 line between the two cells is clear and distinct and quite different 

 from the "Segnientgrenzen" of the adult. It should be remembered 

 loo that in young 0. dioica the breaks are frequently absent. The 

 "islands" already referred to furnish evidence that breaks do occur. 



