1875. J 197 [Brooks. 



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 derived 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. (Figure 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 constric- 

 tions 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 be- 

 comes 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 that 

 the developmental history of the genus presents a true example of 

 " alternation of generations." When, however, we have traced back- 

 ward the history of one of the "zooids" which compose a chain, and 

 find that the egg is present at all stages of growth, and is of exactly 

 the same size and appearance as at the time of its impregnation; 

 when we find one organ after another disappearing, until at last we 

 have nothing but a faint trace of a constriction indicating upon the 

 wall of the stolon the position of the future "zooid," the conclusion 

 seems to be irresistible that the animal, which has as yet no exist- 

 ence, cannot be the parent of the egg which is already fully formed. 



The life history of Salpa may then be stated in outline as follows : 

 The solitary salpa is the female, and produces a chain of males by 

 budding, and discharges an eg<^ into the body of each of these before 

 birth. These eggs are impregnated while the " zooids " of the chain 

 are very small and sexually immature, and develop into females which 

 give rise to other males in the same way. 



After the foetus has been discharged from the body of the male 



