Vou. 2] Ritter—The Pelagic Tunicata. 69 
by the Albatross (data as to time and locality lacking, but cer- 
tainly Pacific Ocean material) a total length of 60 mm. was 
reached, the body here, exclusive of the processes, being 40 mm. 
These last were somewhat larger than the largest Challenger 
specimens of echinata. That these robust aggregate zooids belong 
with the echinata form of the solitary generation may be held 
as probable, although nothing less than absolute proof of this 
will warrant associating them positively in classification. 
Now a few more words in support of my opinion that we have 
here a ease of extreme, for this group of animals, individual vari- 
ation, or fluctuation, rather than a true variety, or ‘‘elementary 
species.’’ In the first place, as to the echination of the test. 
It is doubtful if this is ever wholly absent in S. fusiformis- 
runcinata. Certainly if it is, it is so only exceptionally. So 
far as the evidence goes on this point, it is to the effect that the 
thickening of the test at the posterior end, the prominence of 
the ridges, and the serrations increase with the size, and pre- 
sumably with the age, of the zooids in both generations. But 
more extended and exact information is needed here. There 
are undoubtedly some observations opposed to this supposition. 
For example, I have one specimen of the solitary generation 
taken at Bolinas Bay, California, November 18, 1895, which, 
although seareely more than half the size of the largest echinata, 
yet possesses the longest, heaviest three posterior processes I have 
seen in any zooids whatever. But here the serrations are almost 
entirely wanting. In this specimen, too, the muscle plan is 
strictly that of fusiformis-runcinata—that is, the anterior three 
and posterior two are fully fused. And here I would say that 
the examination of a large number of specimens with reference 
to the point has failed to discover a single instance of the sepa- 
ration of these muscles in a small zooid. I consequently incline 
to the opinion that the separation of the muscles is an age char- 
acter. But here, too, more positive evidence is needed. My pro- 
visional conclusion is, then, than echinata is an old age form of 
fusiformis-runcinata. 
In view of the usually clear delimitation of species in Salpa, 
the question of the status of echinata is especially interesting. 
It well deserves more extensive and critical examination. Ap- 
