ZOOLOGY AND BOTANY, MICROSCOPY. ETC. 629 



MoUuscoida. 

 o. Tunicata. 



Alternation of Generations in Salpae.* — Dr. 0. Seeliger discusses 

 the problem of the origin of alternation of generations in Salpae. He 

 reviews the various statements and interpretations of the facts, especially 

 those of Todaro, Brooks, Salensky, and Ulianin, but is dissatisfied with 

 all. The alternation has arisen from an original " hypogenetic " process 

 in the following way. A portion of the hermaphrodite system became 

 degraded and gave off buds, with which processes of the parent ectoderm 

 and endoderm co-operated. The remaining portion of the reproductive 

 organ in the parent organism retained its normal function. In 

 Pyrosoma, the forms produced by budding retained both modes of multi- 

 plication. 



At a further stage, not a portion merely, but the whole reproductive 

 organ of the original solitary fjrm was used up in budding. An asexual 

 generation thus arose, as at present exhibited in Salpse. At the same 

 time, with increasing dimorphism of generations, the asexually produced 

 individuals lost the power of budding. 



In Pyrosoma, the stolo prolifer forms only about six individuals, each 

 of which has in the ovarian strand one large ovum and a considerable 

 number of undifferentiated reproductive cells. In Salpa, on the other 

 hand, the stolo prolifer of the solitary form gives off many hundred 

 closely apposed buds, in which only a few cells are found in the ovarian 

 strand able without special delay to form the hermaphrodite system. In 

 the chain Salpa there are no further cells, as there are in Pyrosoma, in a 

 position to become the mesoderm of fresh buds. Furthermore, in the 

 close disposition of the Salpa buds, there is neither space nor nutrition 

 for another generation of buds, even if ectoderm and endoderm should 

 still retain the embryonic character which would admit of their taking 

 part in a budding process. 



;3. Bryozoa. 



Polyzoa of the Voyage of H.M.S. ' Challenger.'f— Mr. A. W. Waters 

 has prepared a short supplementary report on the Polyzoa, in which he 

 adds particulars of various structures and organs not previously noticed. 

 The most interesting discovery appears to be that of the presence of a 

 common parenchym cord surrounding the zooecia of Betepora columnifera. 

 Mr. Waters thinks that we must not be satisfied merely with the shape 

 of the operculum, but we must give special attention to the way in which 

 it is attached and articulated, and the connection through the rosette 

 plates must be more studied. Too much attention seems to be attached 

 to peristomial characters. 



Bryozoa of New South Wales.| — Mr. A. W. Waters describes a 

 number of incrusting species of Bryozoa obtained off Green Point, Port 

 Jackson. Some of these are new, and others, being represented by better 

 specimens than heretofore, are now more fully described. 



Reproduction of Ctenostomatous Bryozoa. §—M. H. Prouho gives 

 an account of some observations on the reproduction of Alcyonidium 



* Jenaische Zeitschr. f. Naturwiss., xxii. (1889) pp. 399-414. 

 t Reports of the Voyage of H.M.S. 'Challenger,' xxxi. pt. Ixxix. (1889) 41 pp. 

 (3 pis.). J Ann. and Mag. Nat. Hiet., iv. (1889) pp. 1-24 (3 pis.). 



§ Comptes Kendus, cix. (1889) pp. 197-8. 



