ASCIDIACEA TRANSVERSE FISSION. 449 



(the intestinal loop and the heart) remain unaffected by degeneration, 

 and, should the conditions of existence again become more favourable, 

 this posterior half is able to regenerate the anterior part. An increase 

 in the number of individuals forming the colony, by means of division, 

 may even be connected with this regeneration. The yellow body then 

 becomes lobate, and divides into several parts, each of which develops 

 into a new Ascidian. The details of these interesting processes are, 

 however, still unknown. 



The occurrence of such far-reaching regenerative processes and the 

 capacity for asexual reproduction in the Tunicata at first sight seems 

 surprising, when we take into account their comparatively complicated 

 organisation and their near relationship to the Vertebrata. We must, 

 however, remember that the same capacity is found in the Annelida 

 and the Echinoderma, groups which, in the condition of their 

 organisation, may at least be compared with the Tunicata. 



1. Social and Composite Ascidians. 



The asexual reproduction which takes place in these groups is 

 usually called budding. In the Polyclinidae , however, asexual 

 multiplication takes place through the segmentation of the post- 

 abdomen. This kind of reproduction, therefore, must, strictly 

 speaking, be defined as transverse fission, and must be considered 

 as distinct from budding. 



A. Reproduction through Transverse Fission. 

 This is the kind of multiplication which was defined by GIARD 

 (No. 57) as " bourgeonnement ovarien " and which has become better 

 known through the researches of KOWALEVSKY (No. 61) in connection 

 with Amarouclum proliferum. 



[Since this description was published, further investigation of the budding 

 processes in the composite and the social Ascidians has shown us that, while 

 the account given in the following pages is correct in so far as it derives all 

 the important internal organs from the inner sac, yet it obscures the actual 

 state of affairs by always speaking of this structure as entodermal. While it 

 is probably true that this inner sac is derived from the entoderm in most cases, 

 yet, in one group, the Botryllidae, if the observations of HJORT (No. XIV.) and 

 PIZON (No. XXVI.) are correct, this does not appear to be the case. These 

 observers find that the stolon is purely ectodermal, the epicardia arising from 

 the peribranchial sacs of the parent which, in the first instance, i.e., in the 

 larva, are of ectodermal origin. From this ectodermal epicardium, the bud 

 arises much in the way described above. Thus we find that, in one family, all 

 the organs of the bud are of ectodermal origin, while, in the majority, they 

 arise from the entoderm. ED.] 



GG 



