BUDDING IN TUNIC AT A. 65 



the larva gives rise to a bud on only one side of the body 

 (the right side) ; and, although the buds of successive 

 generations of buds are usually paired, there is always a 

 certain asymmetry in their development : the buds on the 

 right side being always further advanced than those on the 

 left (Oka). The asymmetry which characterises budding 

 in these more primitive cases seems to me to have con- 

 siderable significance, and to point to the conclusion that 

 the power of bud-production was originally restricted to 

 one side of the body ; in other words, that the production 

 of twin-embryos or twin-zooids which characterises the 

 Didemnidse and Diplosomidae is a primitive phenomenon. 



Now Salensky's recent work (26, 27) upon the develop- 

 ment of the twin-embryo of Diplosoma shows conclusively 

 that this is a true case of embryonic fission, although the 

 process is condensed and modified in various particulars. 



The conclusion, therefore, is inevitable that all the types 

 of budding in the Tunicata are ultimately referable to an 

 ancestral process of embryonic longitudinal fission, as Bal- 

 four and Uljanin have already suggested. We may also 

 conclude that budding has probably not arisen more than 

 once within the group of Tunicata, since the various types 

 of asexual reproduction found within it form a single phylo- 

 genetic series, and are connected with one another by 

 numerous gradations ; and that while the differentiate type 

 of budding is probably in many respects more primitive 

 than the undifferentiate type, yet that there have been 

 modifications in both directions since budding first arose, 

 leading, in some 4 cases to a secondary simplification of the 

 organisation of the bud, and in others to a slightly increased 

 complexity. 



BIBLIOGRAPHY. 



(1) BALFOUR, F. M. Comparative Embryology, vol. ii. 



(2) BARROIS, JULES. Recherches sur le Cycle Genetique et le 



Bourgeonnement de l'Anchinie. Journ. de V Anat. et de la 

 Physiol., xxi., p. 193, 1885. 



(3) Beneden, Ed. Van, et Julin, Ch. Recherches sur le Mor- 



phologie des Tuniciers. Arch, de Biol.,vi., 1887. 



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