ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 415 



J. v. Boas, as well as other points. As in previously studied cases of 

 castration, there is a very singular want of uniformity in the phenomena 

 observed, which is probably due to the date at which infestation 

 occurred ; and the modifications are not indelible, for in male Paguri, 

 which had been freed from their parasites, the characters of the male sex 

 gradually reappeared at the successive moults. The numerous species of 

 Hippolyte have been described in a way that leads M. Giard to suppose 

 that the castrating influence of parasitism has not been taken into 

 account. 



Fresh-water Crabs of Africa.* — M. A. Milne-Edwards finds that the 

 fresh-water crabs of Africa are all Thelphusidfe ; twenty-five species are 

 enumerated; for a form from Lake Tanganika, a new genus — Platy- 

 thelphusa — is instituted. The species is called P. armata. 



Photospheria of Nyctiphanes norvegica.t — Messrs. E. Vallentin 

 and J. T. Cunningham have investigated the structure of the phosphores- 

 cent organs of this Schizopod. They find that the hinder part of each 

 organ is bounded by a layer composed of wavy fibres, which, to some 

 extent, anastomose ; this layer is of considerable thickness, and forms 

 a hemispherical cross, open in front only. It contains no distinguishable 

 cell-areae, and, as it resembles to some extent a tapetum, it may be called 

 the reflector. The external surface is covered by a flat mosaic-like 

 epithelium of polygonal, red pigment-cells. Internally to the reflector 

 is a layer of large cells, each with a large nucleus ; the internal surface 

 of the cellular layer is perfectly smooth, and in the hollow contained by it 

 is a curious fibrillar mass. The fibrils of this are mostly straight, and those 

 that are external are perpendicular to the surface of the cellular layer, 

 while the core consists of two bundles of straight fibrils which cross at 

 right angles, and other bundles set in other directions. In front of the 

 fibrillar mass are a few flat cells, which belong to the cellular layer, and 

 in front of these is a bi-convex lens ; this is perfectly homogeneous and 

 highly refringent, and, as its diameter exceeds that of the fibrillar mass, 

 it rests on the edges of the cellular layer. In front of the lens is a layer 

 of cellular tissue, which contains a ring of circular fibres, running round 

 the edge of the lens. The cells of this layer, which may be called a 

 cornea, are much smaller and more regular than those of the posterior 

 cellular layer. The differences between the photospheria of the body, 

 which have just been described, and that of the ocular peduncle is con- 

 siderable ; in the latter, every layer, with the exception of the straight 

 fibrils and the reflector, is continuous with the epidermis. This would 

 appear to indicate that the organ is formed by differentiation of parts 

 from a simple thickening of the epidermic layer of cells. The reflector 

 is probably a specialization of subepidermic mesoblastic tissue, and the 

 posterior cellular layer a specialization of the deepest portion of the 

 epidermic thickening. The other photospheria are advances in speciali- 

 zation. 



With regard to the function of these organs, the authors admit, with 

 reservation, that their activity is under the control of their possessor; 

 nothing like continual luminosity was ever observed. When an animal 

 was crushed beneath the fingers certain particles were luminous, and re- 

 mained so till they were dry. When crushed under a cover-glass it 



* Ann. Sci. Nat., iv. (1887) pp. 121-49 (3 pis.) 



t Quart. Journ. Micr. Sci., xxviii. (1888) pp. 319-41 (1 pi.). 



