GENERAL CONSIDERATIONS ON THE TUNICATES. 51*S 



composite Ascidians. We must await the result of farther researches 

 before coming to any definite conclusion. 



In any case, the development of t lie buds must always lie considered 

 quite apart from embryonic development, since these two methods 

 of development are to be traced back to different principles. In 

 the embryo, the primary organs arise anew from an originally 

 undifferentiated mass of blastomeres, while in budding, which is 

 evidently deducible from division, parts of the most important 

 primary organs are taken over from the organisation of the parent 

 into the bud. Although the literature on the budding of the Tuni- 

 cates at present is far from supporting the statement that all the 

 more important organs in the bud or the stolon are to be derived by 

 abstriction from the corresponding organs of the parent, indications 

 are not wanting that the solution of the problem as to the origin of 

 the organs of the bud is to he sought in this direction (p. -1ST). It 

 appears, for instance, that the strands which, compose the rosette-like 

 organ of Doliolum are direct continuations of all the more important 

 organs of the parent. In the four primary Ascidiozooids of Pyrosoma 

 dso, the peribronchial tubes and the pericardial rudiment of the 

 Cyathozooid are directly continued. It may be mentioned further 

 that, according to Koyvalevsky, the peribranchial tubes in the stolon 

 of Salpa are derived from the atrium of the parent. These state- 

 ments which, however, are in direct contradiction to many observa- 

 tions on other forms suggest that none of the more important organs 

 airist anew in the bud, but that all the mort important rudiments of 

 organs pass over from the parent into the stolon and thence into the 

 buds, while tin actual new formation of organ-rudiments takes place 

 only in the embryo. The nervous system would probably have to be 

 considered as an exception to this rule. Since we know that the 

 brain of the Ascidian can be regenerated after excision, it appears 

 possible that it arises anew also in the buds, though probably only 

 from the ectoderm. 



Turning to the embryonic development, we rind that the different 

 divisions of the Tunica ta here also vary greatly. The embryouic 

 development of the Salpidae is, indeed, so little understood that we 

 are hardly in a position to say anything definite about it. When we 

 see that, according to Salensky, all the species examined show 

 important variation in their methods of development, it is evident 

 that there is here an ample Held for further research.* We may. 



[*See footnote, p. 123 and pp. 445-446.— Ed.] 



