430 W. E. RITTER AND M. E. JOHNSON 
the present study, of considering this point,nor do we propose 
now to go into it extensively. However, our results on the growth 
and mechanical factors involved in producing the wheels of Cy- 
closalpa seem to have so much bearing on the question, that we 
can hardly pass it by without notice. The resemblance between 
such a figure of the Cyclosalpa wheel as, for example, that given 
by Brooks (93, pl. 1, fig. 2), and reproduced by Delage and Hé- 
rouard (p. 203, fig. 151) and a figure of an early Pyrosoma colony 
like 15, (pl. 31), by Huxley (’59) is considerable and not unnaturally 
suggests true heredity kinship. The moment, however, one comes 
to look into the details of how each group comes about ontoge- 
netically rather than phylogenetically, he finds them so different 
that his imagination is balked at an attempt to interpret them 
as both referable to a common hereditary operation. In the first 
place Brooks seems never to have observed the fact that the 
Cyclosalpa wheel is at the outset bilateral. None of his published 
figures give any intimation of this, nor does he refer to it in his text. 
For instance, the two figures, 8 and 9, pl. 2, of his latest publica- 
tion (Brooks, ’08) represent wheels of C. floridana, and C. pinnata 
as though they were perfect—as though the zooids were disposed 
in exactly the same way throughout the circuit. We would not, of 
course, assert that he did not draw just what he saw in these 
two instances, especially since we have had no chance to examine 
the wheels of C. floridana, and have seen but a single one of C. 
pinnata. In the one specimen of C. pinnata which we have, 
attentive study finds that two zooids on opposite sides of the cir- 
cuit have slightly different positions from the others. These 
probably indicate where the axis of the chain lay; but the de- 
parture from perfect regularity is so slight and of such a char- 
acter that it might be easily overlooked had one not discovered, 
by studying the formation of the wheels, what their real nature 
is. In C. affinis the bilaterality of the wheels is probably never 
wholly obliterated. 
The first four ascidiozooids in Pyrosoma, on the contrary, 
stand in single file as do the Salpa zooids before the deploying 
point is reached and the radial order is taken on by the swinging 
around of the file so that number four comes to be adjacent to 
