88 Papers from the Marine Biological Laboratory at Tortugas. 



muscle 7, while it does unite with muscle 8 and with its fellow of the op- 

 posite side, on the ventral middle line. 



Muscle 7 is in the organ of attachment in 5. pinnata, S. affinis, and S. 

 floridana, and probably in 5\ virgula. In 5". pinnata and 5". affinis it is 

 united ventrally to muscle 6, but it is not so united in 5". floridana. Dor- 

 sally it crosses the middle line close to, but not united with, muscle A in 5". 

 pinnata and 5". affinis, while in 5". floridana it unites dorsally with muscle 

 9 to form the median dorsal muscle B. It is no doubt homologous in all 

 the aggregated cyclosalpas, and also homologous with muscle 7 of the 

 solitary cyclosalpas. 



Muscle 8 is a complete and independent ring in S. pinnata; prolonged 

 ventrally into the organ of attachment in 6". affinis; united with muscle 6 

 on the ventral middle and with muscle 9 laterally in S. floridana, it is 

 homologous with muscle 8 of the solitary forms. 



I am not able to identify the muscles posterior to 8 in the various 

 aggregated forms with each other or with those of the solitary forms with 

 any confidence, as the various species are much specialized in this region. 



In S. pinnata the muscle that I have marked 9 crosses the middle line 

 of the dorsal surface close to, but not united with, muscle 8. In S. affinis 

 it crosses the dorsal middle line independently of and at a distance from 

 muscle 8. In S. floridana it crosses the middle line of the ventral surface, 

 and unites dorsally with muscle 8, and then with muscle 7 to form muscle 

 B, which crosses the dorsal middle line close to but independently of 

 muscle A. 



Muscle 10 is a circular muscle that seems to be homologous in 5". 

 pinnata, S. affinis, and 5". floridana, and it is joined to muscle 9 by the oblique 

 muscle C. 



The results of .the study of the muscles of the various species of Cyclo- 

 salpa in the solitary and the aggregated form may be summarized as fol- 

 lows : The muscles are homologous, and in most cases the homology can be 

 traced without difficulty, while it is more obscure in other cases; it is most 

 easy to trace in anterior ends of the bodies, while the specialization is 

 greater, and the homology more obscure, in the posterior region of the 

 body. There is a very complete series which connects the simplest and 

 most primitive form the solitary 5". pinnata with the most specialized 

 form the aggregated 5". floridana. 



