346 BULLETIN OF THE 



the normal course of development and omitting the larval stage en- 

 tirely, we cannot expect it to throw any additional light upon this 

 question. 



The presence of a placenta is of course only an analogy with the 

 Mammalia, since the resemblance is simply functional and not in any 

 sense morphological.* 



* A memoir by Todarro (Sopra lo Soiluppo, e 1' Anatomia delle Salpe, del Dott. Fran- 

 cesco Todarro, Roma, 1875), on the development of Salpa, reached me after I had fin- 

 ished writing my own account. In this he refers to an abstract published by Kowalev- 

 sky in 1868 (Nachrichten von der K. Gesellschaft der Wissenschaften. Gottingen, 1868, 

 p. 407 - 415) ; as this is not referred to by Kowalevsky in any of his later papers on the 

 development of theTunicata, and is omitted from the index of the Nachrichten for that 

 year, it had escaped my notice until my attention was called to it by the reference in 

 Todarro's paper. It is simply a very brief and condensed preliminary abstract, without 

 figures, and although it agrees in general with my own observations, it seems to conflict 

 with them in several important particulars. The developmental history of Salpa is so 

 very complicated that it is hardly possible to decide, in the absence of figures, exactly 

 how much weight to attach to this apparent lack of agreement ; and although anything 

 upon the embryology of the Tunicata by this distinguished embryologist, to whom we 

 owe so large a part of our knowledge of this subject, must be regarded as having the 

 highest authority, it does not seem advisable to rewrite my paper in order to refer to 

 views which, from the condensed way in which they are stated, and from the lack of 

 illustrations, it is very possible that I may have misunderstood. In a few cases, however, 

 the want of agreement is too evident to be explained in this way. He says (pp. 109, 

 110) "that no direct communication, such as has been stated by some to exist, is to 

 be found between the cavity of the placenta and the body cavity of the mother.'' 



The animal which contains and gives birth to the embryo is, according to our view, 

 not the mother, but the male nurse. Regarding the existence of a communication be- 

 tween the body cavity of the nurse and the inner chamber of the placenta, I can only 

 reiterate my statement that, at all stages, from the first appearance of the cavity of the 

 gastrula until the embryo is fully formed, the blood of the nurse can be seen passing 

 into and out of the cavity of the placenta. It is possible that there is a difference be- 

 tween the various species in this respect, for Vogt and Todarro agree with Kowalevsky 

 in stating that at one period at least there is no such communication, while most of 

 the other writers are equally confident that the facts are as I have stated them. 



His account of the formation of the stolon also differs somewhat from mine. He 

 says (pp. 412, 413) that this is made up of the following parts : (1) the outer wall, de- 

 rived from the outer tunic of the parent ; (2) the digestive tube, derived from the 

 intestine of the parent ; (3) two cloacal tubes, continuations of the posterior ends of 

 the cloaca of the parent ; (4) a bunch of cells, which gradually lengthens, becomes tubu- 

 lar, and gives rise to the ovaries of the chain-salpaa ; (5) a tube which becomes converted 

 into the nervous systems of the chain-salpae. According to my observations, the diges- 

 tive tube is not derived directly from the digestive organs of the parent, but from the 

 pericardium. The two cloacal tubes mentioned are without doubt the safne as those 

 which I have called the sinus-chambers of the stolon ; and the fact that the blood cir- 



