38 



Salpce, whose existence was first demonstrated by Chamisso twenty 

 years ago, and which have formed the basis of the theory of " alter- 

 nate generations." 



The author refers to IM. Krohn as the only riter who has pre- 

 viously entered thoroughly into this subject ; but while he bears 

 testimony to the extreme accuracy of M. Krohn's statements, he sub- 

 mits that, as the latter are published in a very condensed form only, 

 and without figures, they cannot affect any value that may attach 

 to his own independent researches. 



The forms of Salpa examined were the S» democrcUica and S, 

 mucronata. 



The author first describes their outward form, and shows that 

 they are so different in appearance and in some points of organiza- 

 tion, as to fully warrant the assumption (if they belonged to any 

 other family) that they are different species. He then proceeds to 

 describe the various organs in detail ; first, however, discussing the 

 proper nomenclature of the sides and ends of these animals, a sub- 

 ject on which much confusion has prevailed. Particular attention 

 is called to the existence of an organ hitherto undescribed — a cylin- 

 drical, elongated body, like an internal shell, — here termed the " en- 

 dostyle" which lies in the dorsal sinus, and has hitherto been con- 

 founded with the dorsal folds" of Savigny. A peculiar system of 

 delicate transparent vessels, taking its origin in the stomach and 

 ramified over the intestine, is described and its nature inquired into. 



The organs of reproduction are next inquired into. The young 

 in the Salpa democratica constitute a " Salpa-chain," and are shown 

 to arise by gemmation from a tubular diverticulum of the vascular 

 system of the parent. In the course of their development they take 

 the form of the S. mucronata. 



The young in the Salpa mucro7iata again is shown to be solitaiy, 

 and attached to one point of the respiratory chamber of the parent 

 by an organ which exactly represents in its structure a rudimentary 

 mammiferous placenta, except that in the SalpcB the " villus" is 

 formed by the maternal system, the placental cell" by the fcetal 

 system. But the foetus here is not produced by gemmation, as in 

 the preceding case, but by a true process of sexual generation. 



Every Salpa mucronata contains at one period of its existence a 

 solitary ovum, and a testis, which is a ramified gland surrounding 

 the intestine, and hitherto confounded with the liver. The solitary 

 ovum becomes fertilized, pushed out into the respiratory cavity of 

 the parent, and remains connected with the latter until it has as- 

 sumed the form of the Salpa democratica, when it becomes de- 

 tached. 



Chamisso's formula therefore, " that the parent Salpa produces 

 an offspring different from itself, which again produces an offspring 

 different from itself, but similar to its parent," is perfectly correct, 

 only the word "produce" has two meanings — in the one case signi- 

 fying a process of gemmation^ in the other of true sei'ual generation. 



The author next proceeds to describe the anatomy of Pyrosoma., 

 and to point out its general harmony with that of Salpa. He shows 



