BUDDING IN TUNIC ATA. 59 



reveal in the buds of Botryllus some mode of origin 

 of the nervous system intermediate between that de- 

 scribed by Salensky in the case of Diplosoma and the 

 merely local differentiation of the ectoderm of the sto- 

 lon, which has been observed in Distiplia, Salpa and 

 Pyrosoma. 



The controversy upon the development of the nervous 

 system in the buds of Botryllus raises such wide and im- 

 portant issues that I have thought it worthy of somewhat 

 lengthy consideration. It should also be mentioned that 

 Hjort (10) has recently reiterated the statements contained 

 in his first paper on Botryllus, and gives an additional case 

 [GlossopJiorum) in which, as he maintains, the brain arises 

 from the dorsal (endodermal) tube. A similar origin of the 

 brain has just been described by Ritter'(2i) in the case of 

 the buds ot PeropJwra. 



Doubtful, however, as many points remain, it has, I 

 hope, been clearly shown in the present article that the 

 theory of differentiated germinal layers has not been proved 

 inapplicable to the phenomena of blastogenesis in the 

 Tunicata. Many of the earlier statements upon the subject 

 were undoubtedly inconsistent with the general theory, but 

 they have been modified to a great extent by the more 

 exact researches of recent years. Development by budding, 

 although presenting extensive peculiarities in the details of 

 organogeny, seems on the whole to agree with embryonic 

 development in all fundamental points. No single fact, 

 inconsistent with the general applicability of the germ-layer 

 theory of development, has been hitherto established in the 

 case ol Tunicate buds. 



3. YVic Types of Budding. — A classification of the various 

 modes of budding may be made from different points of 

 view. Usually the existence or absence of a stolon is made 

 the basis of classification ; but such a course seems quite 

 arbitrary, and raises into fundamental importance a feature 

 altogether secondary and unimportant from a morphological 

 point of view. Some authors are inclined to connect the 

 two processes of budding exhibited by the cyathozooid of 

 Pyrosoma and by the Polyclinidae, on the ground that these 



