276 PROFESSOR PAVESI. 



Bonn, Avho is now in Naj^les, I make them the subject of this 

 note. 



The season (December and January) was favorable for 

 studying, besides the circulation in the adult Ascidians, the 

 mode of circulation and nutrition in the embryos, which had 

 not yet been observed. I intend chiefly to speak of the com- 

 pound embryos discovered by M. Savigny,^ better studied by 

 Professor Huxley," and lately by M. Kowalewsky.^ It is 

 established that from the ripe egg, after a partial segmenta- 

 tion of the vitellus, there appears an incompletely organized 

 embryo, the so-called " cap " or cyathozooid of Professor 

 Huxley, which gives rise by gemmation to four other zooids 

 (ascidiozooids of Huxley) ; these latter enlarge, develope, and 

 surround the cyathozooid, which at first is much larger than 

 they are, but diminishes, and finally disappears at a later 

 stage. The four embryos are united to one another, and to 

 the cyathozooid, by means of a cord. This cord is attached 

 to the cyathozooid, and passes, after a short interval, to the 

 nearest embryo, attaching itself a very little below the gan- 

 glion ; but it recommences at the other surface of the same 

 embryo, and passes from the lower end of the endostyle to 

 the ganglion of the neighbouring embryo, and thus is con- 

 tinued through the series to the last embryo, which has but 

 a single connection." This cord, so well described by Pro- 

 fessor Huxley, has been, j^erhaps, seen also by M. Savigny, 

 since he draws in one of his figures a very short cord, of a V 

 shape, indistinctly, which unites the four embryos, but he 

 makes no mention of it in the memoir and in the explanation 

 of the jDlates. 



M. Kowalewsky has pointed out that a heart exists in the 

 cyathozooid, which, in fact, is nothing else but a "nurse/' 

 similar to the generating larvse of many inferior animals. 



I have observed, in examining this heart of the " nurse," 

 that it has the appeai-ance of a tube, is very transparent, and 

 that it may be seen in process of development lying in a more 

 spacious cavity than itself, having definite walls like a peri- 

 cardium, elongated, and broadened at the extremities. The 

 heart is attached to this pericardium over one entire surface, 

 but is free in the rest of its extent. It is placed obliquely a 

 very little below the external layer of the " nurse," that is to 

 say, quite superficially, in such a way that it may sometimes 

 be seen, when the nurse is turned on its side, at the edge, or 



^ ' Memoirs sur les Animaux sans vertebres,' ii part, ii mem., 1816. 



- " On the Development of Pyrosoma," ' Annals and Magazine of Nat. 

 History,' 1860, January. 



^ ' Entwickelungsgescbiclite der Pyrosoma,' Gottinger Nachricliteu, 1868, 

 p. 401. Confer. ' Ai-chiv f. Naturg.,' 1869, p. 103, Bericht d. Mollusken. 



