ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 795 



Ovaries of Actiniae.* — R. Hertwig finds in CoraUimorpJius rigidus 

 that the smallest ova form groups of 2-4 cells between the bases of 

 the epithelial cells, and that the larger reach almost to the surface of 

 the epithelium ; an egg-cell taken in the act of passiug outwards was 

 seen to have part lying in the mesoderm and part in the endoderm ; 

 the two halves were separated by a constriction which was sufficiently 

 deep to affect the form of the nucleus. Young egg-cells are con- 

 nected with the epithelium by a short cord ; when they leave this 

 region their basal ends first pass into the mesoderm, and soon after 

 the nucleus follows that portion. The filainentar apparatus of the 

 egg-cell, which was only a temporary condition in this form, was more 

 lasting in Halcampa clavus, a conical protoplasmic cord passing from 

 the egg through the supporting lamella to the epithelium. Attention 

 is directed to the peculiar form of the epithelial layer investing the 

 egg, and to the curious fact that a similar phenomenon is to be ob- 

 served in the Acraspedota, where the ova are likewise of endodermal 

 origin. 



Skeleton of Madrepores.f — The law of multiplication of the 

 septa in hexaradiate corals, as first stated by Milne-Edwards and 

 Haime, has gained a general if somewhat qualified acceptance. 

 Schneider and Rdtteken have proposed to modify it as regards the 

 later and more puzzling stages of development. Semper seems to 

 doubt the possibility of establishing the truth of any such formulae, 

 in the presence of the many and intricate variations which even the 

 individuals of one species of coral may display. In his beautifully 

 illustrated memoir on Astroides, Lacaze-Duthiers scarcely enters on 

 the discussion of this question. We cannot cite any other zoologists 

 who have made serious contributions to the subject. 



G. v. Koch, however, who for years has studied the development 

 and structure of the skeleton of the Anthozoa, now comes forward to 

 introduce order where before there was chaos. Neither the law of 

 Milne-Edwards nor that of Schneider are, in his opinion, supported 

 by facts. Semper's scepticism has a certain justification, but must 

 also be rejected. It may be accounted for as follows : — in one or 

 more primary sectors the formation of new septa is liable to sustain a 

 check ; thus septa of the second cycle belonging to such a sector may 

 resemble those of the third cycle elsewhere in the same coral, and so 

 with other cycles. Or, otherwise expressed, a hurried or retarded 

 development of certain septa may here and there occur. Our 

 author's hypothesis, wherein he sums up the general result of his own 

 investigations, is certainly very simple and intelligible : — Throughout 

 the Hexacorallia, both Imporosa and Perforata, an approximately con- 

 temporaneous formation of septa takes place within all the chambers 

 of the calyx, so that the septa of each added cycle are equal in 

 number to all the previous septa. Exceptions must be referred to 

 direct modification or to inherited changes in the growth of the whole 

 animal. 



* SB. Jenaisch. Gesell. Med. u. Naturwiss., 1881, pp. 18-20. 

 t Gegenbanr's Morph. Jahibueh, viii. (1882) pp. 85-9G (1 pi.). 



