448 TUNICATA. 



[S. pinnata, S. bicaudata, etc.), as the homologue of the secondary 

 gill-clefts in the Ascidians (branchial stigmata). We do not think 

 there are sufficient grounds for such an explanation, since these 

 invaginations, which were already known to Fol, may also be 

 secondary acquisitions resulting from the need for increasing the 

 respiratory surface. We have pointed out above that the condition 

 of Appendicularia is probably not to be regarded as primitive. 



Some statements as to the occurrence of a true coelom in the 

 embryos of the Salpidae have still to be noticed. Todaro (No. 107) 

 considers that the coelomic sacs originated through dehiscence takintr 

 place in a mesodermal layer surrounding the intestine. According to 

 Salensky, a cavity first arises in each of the already distinct muscle- 

 hoops, and this cavity also is considered as the equivalent of the coelom 

 in the Vertebrates [i.e., of the cavities in the primitive segment plates, 

 p. 445).* 



The origin of the pericardial sac may perhaps, according to 

 Salensky, be traced hack to the mesoderm, whereas, in the 

 Ascidiacea, it is of entodermal origin (p. 368). [Entodermal accord- 

 ing to Korotneff, see footnote, p. 432]. 



II. Asexual Reproduction. 



Asexual reproduction, both by fission and budding, is of wide 

 occurrence among the Tunicata, and frequently leads to the forma- 

 tion of stocks. Before describing these reproductive processes, we 

 must point out that the capacity for regeneration also occurs to a 

 large extent in this class. The experiments made by Loeb and con- 

 tinued by Mingazzini have shown that solitary Ascidians (Ciona 

 Intestinal is) are capable of regenerating distinct portions of the body. 

 If, for example, the central nervous system is removed artificially, it 

 can be regenerated. In some cases, similar processes of regeneration 

 seem to occur normally. This was observed by Della Valle (No. 

 70) in colonies of Diazona violacea, in which, under unfavourable con- 

 ditions, the anterior part of the body (the branchial sac and other 

 organs) degenerate in the individuals of the colony. There is then 

 found in this region an accumulation of yellow mesoderm-cells filled 

 with nutritive material. The organs of the posterior half of the body 



* [Brooks (No. I.) eonsideis the transitory body-cavity of Salpa as a re- 

 opening of the follicular cavity, and this latter he attempts to homologise with 

 the cleavage-cavity of the normal gastrula. He thus regards the body -cavity 

 of Salpa as the equivalent of the primary body-cavity (cleavage-cavity), and 

 not as the secondary body-cavity (coelom proper). The cavity becomes filled 

 later with mesenchyme -cells from which the muscle-hoops arise. — Ed.] 



