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 S. pinnata, S. affinis, and S. 
floridana, and probably in S. virgula. In S. pinnata and S. affinis it is 
united ventrally to muscle 6, but it is not so united in S. floridana. Dor- 
sally it crosses the middle line close to, but not united with, muscle A in S. 
pinnata and S. affinis, while in S. 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 S. affinis; united with muscle 6 
on the ventral middle and with muscle 9g 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 S. 
pinnata, S. affinis, and S. 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 S. pinnata—with the most specialized 
form—the aggregated S. floridana. 
