186 RITTER. (VoL. XII. 
But I have been unable to get decisive evidence of such a 
relation between these elements; and the structure of the 
youngest undoubted female polycarps found does not strengthen 
the conjecture, for in these the ova are in different stages of 
development, but even the smallest show the characteristics of 
ova. Fig. 51, Pl. XV, represents such a polycarp. It has not 
yet advanced sufficiently to have pushed its way from the body 
space into the peribranchial chamber. Certain clusters of a 
few cells larger, more deeply stained, and more granular than 
the other blood cells, Fig. 54, Pl. XVI, I suppose to be the 
male sexual cells; but this too is not beyond question. 
As has been pointed out in describing the species, the poly- 
carps have a rather regular position on the ventral side of the 
zooids, on each side of the endostyle and not far from it. In 
other words, they occupy undoubted determinate positions. 
With the sex cells at first apparently wholly subject to the 
movements of the blood, one would much like to know how it 
comes about that their final points of attachment, where they 
develop into the polycarps, are always nearly the same. That 
they are in the ventral part of the zooids suggests that the 
greater weight of the cells, while still swimming in the blood, 
prevents their being carried into the higher parts to become 
attached; but that indicates nothing as to why they should 
become arranged so regularly on each side of the endostyle. 
Unless we may assume determinants for these particular cells 
of a considerably higher grade of intelligence than is generally 
attributed to these convenient phantoms, it would seem that 
there must be some physical or chemical condition in the 
membrane in the region where the polycarps are situated that 
attracts to it the sex cells from the blood when they happen 
to be carried near it. 
With the young sex cells entirely subject to the movements 
of the blood, and as a consequence liable to be carried to 
various parts of the colony, —into one zooid or another, — it is 
interesting to notice how completely, from the sexual point of 
view, at least, the colony, and not the ascidiozooids composing 11, 
is the individual. 
