1895. NOTES AND COMMENTS. 231 



that the outUnes of the suggested system become clearly marked. 

 The following subdivisions were proposed, and were based by Mr. 

 Garstang upon the scheme of Mr. Lahille : — 



Perennichordata Appendicularians. 



Caducichordata. 



I. Thaliacea. Protostigmata undivided ; cloaca posterior. Pelagic, 

 i. Myosomata. Musculature in bands ; lateral atria small ; 

 internal longitudinal bars absent. 

 e.g., Doliolum, Salpa, Anchinia. 

 ii. Pyrosomata. Musculature diffuse ; lateral atria large ; internal 



longitudinal bars present. 

 e.g., Pyrosoma. 

 II. Ascidiacea. Protostigmata subdivided into rows of secondary 

 stigmata; cloaca dorsal. Fixed, 

 i. Stolidobranchia. Internal longitudinal bars present ; bars solid 

 and ribbon-shaped, 



e.g., Botryllus, Cynthia, Goodsiria. 

 ii. Phlebobranchia. Internal longitudinal bars present ; bars 



tubular. 



e.g., Pevophora, Ascidia, Diazona. 

 iii. Aplousobranchia. Internal longitudinal bars absent; horizontal 



membranes present. 



e.g., Clavelina, Distaplia, Amarcecium. 



In the discussion which followed the reading of this paper the 

 president genially acknowledged his conversion as to the relationship 

 and position of Pyrosoma, but was still doubtful whether the time had 

 come for discarding the old and convenient subdivision of the 

 Ascidiacea into " simplices " and " compositae " in favour of the 

 system now advocated. 



The subject was continued in a paper on Budding in Ascidians 

 by Professor Ritter, of CaUfornia. It was again shown that several 

 compound Ascidians are less closely related to one another than to 

 certain simple Ascidians which are themselves widely different from 

 one another in internal organisation. But the paper was chiefly 

 interesting as a contribution to the controversy concerning the 

 bearings which budding in Tunicata has on the germ-layer theory. 

 Professor Ritter's observations have led him to the conclusion that 

 " in embryonic development the ectoderm produces the matrix of the 

 test, the peribranchial sacs, and the central nervous system and hypo- 

 physeal duct, while in the bud we see these four parts of the animal 

 produced by the inner or so-called endodermic vesicle." In this 

 phenomenon we have what Professor Ritter calls an excellent case of 

 " developmental opportunism." The effect of influences bearing 

 upon the bud in its development has overcome all the hereditary 

 tendencies and scruples of its tissues ; though it is rather the means 

 than the end which has undergone modification. According to a 

 theory of Seeliger's, which Professor Ritter revives, this derivation of 

 primarily ectodermal organs from endodermal tissues may possibly be 

 due to the fact that the ectoderm is already specialised as a test- 

 producing organ at the time of bud-production. 



