ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 797 



Development of Alcyonaria.* — A. Kowalevsky and A. F. Marion 

 have studied the development of two species of Clavularia and of 

 Sympodium coralloides ; they find that, as regards the segmentation 

 of the ovum, which has never yet been completely observed in an 

 Alcyonarian, the fecundated ovum of C. crassa remains for some time 

 without dividing, and the ordinary histological reagents fail to demon- 

 strate the presence of any nucleus, though, after segmeutation, the 

 nuclei are, notwithstanding their small size, easily recognizable. There 

 would appear to be so rapid a division that no two-sphere stage is to 

 be made out, six segments being the smallest number that can first be 

 recognized. A peripheral and a central mass are easily separable from 

 one another, and the former soon gives rise to a well-marked ecto- 

 dermic layer; the endoderm is not slow in its appearance, and the 

 store of yolk becomes rapidly used up. The larva having become 

 fixed, its narrower end is depressed, and gives rise by invagination to 

 an oesophageal sac, the bottom of which becomes pierced and forms a 

 means of communication between the mesenteric cavity and the exterior. 

 Meanwhile the ectoderm has become thickened by the formation of 

 a layer of connective tissue, which may be regarded as the pseudo- 

 mesoderm. Cells migrating from without give rise, in Sympodium, to 

 small calcareous nuclei which become the sclerites ; but in Clavularia 

 the formation of the rudiments of these hard parts is delayed for some 

 time. 



Attention is also directed to the variations in the mode of develop- 

 ment which are exhibited by Sympodium. While some larvas undergo 

 their changes rapidly, others retain their vermiform characters for a 

 longer time, and in these there is no formation of sclerites, but the ecto- 

 derm is differentiated in the manner of Clavularia ; at the base of the 

 pseudo-mesoderm there is formed a fibrous layer which corresponds to 

 an annular muscular band. A large number of primitive mesenteric 

 septa are developed, and the whole of the endoderm is supplied with 

 a layer of longitudinal muscular fibres ; a trausverse section of these 

 larvfe is almost exactly comparable to that of an Actinian. 



Porifera. 



Manual of the Sponges. — The first volume of Bronn's ' Thier- 

 reich,' on the Amorphozoa, written by Bronn himself, was published 

 in 1859. It included the Protozoa and the Sponges. Biitschli having 

 undertaken the second edition of the Protozoa, of which the thirteenth 

 Lieferung has appeared, a revised account of the Sponges is no less 

 imperatively called for. Upon Dr. Vosmaerf has devolved this task. 

 The first Lieferung of his ' Porifera ' is now before us ; its contents 

 are bibliographical and historical, with four plates. A good epitome 

 of the researches of Oscar Schmidt, Eilhard Schulze, and others, is 

 certainly much needed by students, no complete general work on the 

 Sponges having hitherto been issued. 



* Coniptes Kendua, xcv. (1882) pp. 562-5. 



+ • Dr. H. G. Bronn's Klassen und Ordnungen des Thier-reichs. II. Band, 

 Porifera. Neu bearbeitet von Dr. G. C. J. Voamaer.' Winter, Leipzig und 

 Heidelberg, 1882. 



Ser. 2.— Vol. II. 3 n 



