The Pelagic Tunicata of the Gulf Stream. 



/z 



// /o 



end close together, and the anus on the left of the stomach. The loop is loose, 

 and the intestine U-shaped in S\ affinis (text-figure 3) and in S. virgula 

 (Apstein, Die Thaliacea der Plankton-Expedition, fig. i) ; while it is most 

 compact in 5". floridana (plate i, figures i, 2, and 3). In this latter species 

 it resembles the compact nucleus of the ordinary salpas. The comparative 

 anatomy of the intestine is therefore consistent with the view that S. pin- 

 nata is the most primitive and S\ floridana the most specialized among the 

 cyclosalpas. 



The Stolon. In S. pinnata and 5. affinis the stolon is straight, and on 

 the middle line of the ventral surface, under the endostyle, with its free end 

 anterior. I know of no satisfactory 

 account of it in 5\ virgula. In 5\ 

 floridana (plate i, figures i, 2, and 

 3 ) the stolon is twisted into a right- 

 hand spiral, as it is in most of the 

 ordinary salpas, such as S. derno- 

 cratica. In S. floridana it first 

 bends to the left, from the growing 

 end, and then, bending upon itself, 

 turns to the right, so that the free 

 and oldest end is on the right of the 

 middle line, and also on the right 

 of the growing end. The position 

 of the stolon in the various species 



of Cyclosalpa is consistent with the view that 5". pinnata is most primitive 

 and S. floridana most specialized. 



Most, if not all, the species of Cyclosalpa have luminous organs, either 

 in the solitary form alone, or in both the solitary and the aggregated form. 

 The light that is emitted by these organs in -5*. pinnata is so intense that it 

 glows brilliantly under the noonday sun of the Tropics. The organs are 

 similar in structure, but not in position, to those of Pyrosoma. In Cyclo- 

 salpa they are in pairs on the sides of the body, a little nearer to the dorsal 

 than to the ventral surface. In the solitary S. pinnata they extend over the 

 five intermuscular spaces 5-7, 7-8, 8-9, 9-10, and 10-11. In the aggregated 

 S\ pinnata they lie in the intermuscular space 7-8. In the solitary S. flori- 

 dana they occupy the intermuscular spaces 7-8, 8-9, and 9-10, and extend 

 a little beyond 7 and 10. 



THE HOMOLOGY BETWEEN THE MUSCLES OF THE VARIOUS SPECIES 



OF CYCLOSALPA. 



The text-books still continue to give currency to the opinion that the 

 muscles of Salpa are always incomplete, while those of Doliolum are always 

 complete rings, and that this is an important and absolute distinction be- 



FIG. 3. Aggregated Salpa affinis in side view. 



