The Pelagic Tunicata of the Gulf Stream. 
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. 1) ; while it is most 
compact in S. floridana (plate 1, 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 S. affinis the stolon is straight, and on 
the middle line of the ventral surface, under the endostyle, with its free end 
anterior. Iknow of no satisfactory 
account of it im S. virgula. In S. 
floridana (plate 1, 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. demo- 
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 Fic. 3 Aggregated Salpa affinis in side view. 
of the stolon in the various species 
of Cyclosalpa is consistent with the view that S. 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 S. 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 Io. 
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- 
