GENERAL CONSIDERATIONS ON THE TUNICATES. 517 



composite Ascidians. We must await the result of further researches 

 before coming to any definite conclusion. 



In any case, the development of ike bml* must always be 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 Timi- 

 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 be sought in this direction (p. 487). It 

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

 organ of Doliohun are direct continuations of all the more important 

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

 also, the peribranchial tubes and the pericardial rudiment of the 

 (Jyathozooid are directly continued. It may be mentioned further 

 that, according to KOWALEVSKY, 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 organ* 

 arise anew in the bud, but that all the more important rudiments of 

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

 buds, while the 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 embrt/onir development, we find that the different 

 divisions of the Tunicata here also vary greatly. The embryonic 

 development of the Salj>idae is, indeed, so little understood that we 

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

 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 field for further research.* We may, 



[* See footnote, p. 423 and pp. 445-446. ED.] 



