The Pelagic Tunicata of the Gulf Stream. 77 



The following characteristics in respect to the muscles are distinctive 

 of S. floridana: Muscles 4, 5, and 7 meet near the middle line of the dorsal 

 surface to form a common trunk, which does not cross the middle line nor 

 meet its fellow of the opposite side. Muscles 6, 7, 8, 9, and 10 meet on the 

 middle line of the ventral surface to form a common trunk which crosses 

 the middle line and unites with its fellow of the opposite side. Muscle n 

 is independent of other muscles, and its halves are separated from each other, 

 both dorsally and ventrally. Muscle 12 crosses the middle line of the ventral 

 surface, but its ends are independent near the middle line of the dorsal sur- 

 face. Muscle 13 is complete both dorsally and ventrally and free from 

 union with other muscles. It crosses, but does not unite with, muscle 14. 

 Muscle 14 arises on the middle line of the ventral surface, from the middle 

 of muscle 12, in a short longitudinal stem, which quickly divides into a 

 pair of slender muscles, which, running outwards and backwards, bend 

 around on to the dorsal surface and unite with muscle 15. Muscle 15 is 

 a slender muscle which crosses the middle line of the ventral surface and 

 unites, on the dorsal surface, with muscle 14 to form a single dorsal muscle. 



The method of muscle-enumeration that I have employed is the one 

 that is best suited for discussing the homologies of the muscles in different 

 species, and I give a table to show the difference between Apstein's enumera- 

 tion and my own. 



Table to contrast Apstein's enumeration of the muscles of the solitary Salpa floridana 



with author's enumeration. 



BROOKS. APSTEIN. 



Muscle i i on dorsal surface of figures 3 and 4 ; part of 2-3 on ventral 



surface of figure 3. 



Muscle 2 Part of 2 on dorsal surface of figure 4; part of 2-4 on dorsal 



surface of figure 3. 



Muscle 3 2 on dorsal surface of figure 4; I on ventral surface of fig- 

 ure 3. 



Muscle 4 Part of 2 in figure 4 ; part of 2-3 in figure 3. 



Muscle 5 3 in figure 4; part of 2-4 on dorsal surface of figure 3; part 



of 2-3 on ventral surface of figure 3. 



Muscle 6 Part of 2-3 on ventral surface of figure 3. 



Muscle 7 4 in figure 4; 2-4 on dorsal surface of figure 3 ; 4-5 on ventral 



surface of figure 3. 



Muscle 8 5 in figure 4 ; 5 on dorsal surface of figure 3 ; 4-5 on ventral 



surface of figure 3. 



Muscle 9 Muscle 6 in all figures. 



Muscle 10 Muscle 7 in all figures. 



Muscle ii Muscle 8 in all figures. 



Muscle 12 Muscle 9 in all figures. 



Muscle 13 Muscle 10 on dorsal surface in figures 3 and 4. 



Muscle 14 Muscle 10 on ventral surface of figure 3. 



Muscle 15 Not designated nor represented correctly. 



Muscle 16 Not figured nor noted. 



In plate i, figure 4, I give a ventral view of an old embryo 4.5 mm. long, 

 magnified 30 diameters. It is in the same stage of development as the one 

 on which Apstein bases his account of the species. The muscles are es- 

 sentially like those of the adult, except that muscles 12, 13 and 14, are rela- 



