12 Embryology of Salpa. By W. K. Brooks. 
driven up to the blind end where it passes around the partition, 
back through the other chamber to the sinus of the parent. It ia 
of course unnecessary to state that when the circulation of the 
parent is reversed that of the stolon changes also. 
By the formation of the partition above described the tube is 
divided longitudinally into halves, and each half is destined to be 
converted into the series of zooids on one side of the chain. The 
outer wall of the tube, which has been shown to be part of the 
muscular tunic of the parent, becomes the muscular tunics of the 
zooids ; the chambers, which are continuous with the sinus system 
of the parent, form the body cavities or sinus systems of the zooids, 
and the central tube, which is a prolongation of the pericardium of 
the parent, forms the nervous, digestive, and branchial organs of 
the zooids of the chain. It is probable that the cavity of this inner 
tube gives rise to lateral diverticula, which form the cavities of the 
digestive organs and branchial sac of the young, but this point 
could not be determined with certainty, nor could any connection 
between the cavity of this inner tube and any of the cavities of the 
parent be discovered. 
Before the tube becomes differentiated into the organs of the 
zooids, in fact, before there are any indications that the tube is to 
give rise to the chain, two new organs are formed, one in each of 
the sinus chambers of the stolon. These new organs are long club- 
shaped masses of protoplasm, which are not at first attached to the 
tube, but are free within the chambers, and do not seem to be de- 
rived from any of the pre-existing parts of the solitary Salpa, but 
are formed directly from the blood. As the tube grows these organs 
lengthen as well, and soon a row of germinative vesicles is seen 
extending along each of them ; they are the ovaries. (Fig. X., x.) 
At the time that the constrictions, which are the first indications of 
the zooids, make their appearance on the outer wall of the tube, 
each ovary is seen to be made up of a single row of eggs, equal in 
number to the constrictions which indicate the number of the future 
zooids, and as these latter are developed, and their sinus systems 
become separated from the common cavity of the tube, the chain of 
ova divides, so that a single egg passes into the sinus system of each 
zooid, and becomes suspended there by a gubernaculum, by means 
of which it is attached to the wall of the branchial sac, as already 
described. 
Since the chain Salpa at birth always contains an unimpregnated 
ovum, organically connected with its body, and since this egg and 
the resulting embryo are nourished by the blood of the chain Salpa 
by means of a placenta, and since no reproductive organs have ever 
been observed within the body of the solitary Salpa, it seems most 
reasonable to accept the belief that the solitary Salpa is the asexual, 
and the chain Salpa the hermaphrodite sexual generation, and tliat 
