LEYDIG ON DAPHNIID.F.. 27 



course, of a central layer of corium, surrounded on all sides, except at 

 the line where it joins the body, by a chitinous envelope. When the 

 animal is about to shed its skin, the corium secretes around itself, and 

 between itself and the old chitinous layer, a new layer bf chitine; and if 

 an ephippium is being formed, the outer case is produced by the external 

 part of the old layer of chitine, while the chitine which clothed the 

 inner surface of the valve (inner, with reference to the receptacle, 

 though still, of course, in reality, an external skin), is modified into the 

 inner capsule of the ephippium, and the new layer of chitine takes, there- 

 fore, no share in this process. 



As a proof that this view was correct, I cited the fact, that on re- 

 moving the outer valve of a Daphnia, which was about to change its 

 skin, the animal swam away, and the inner ephippial valve remained in 

 the receptacle. M. Smitt seems to doubt whether there is not some 

 mistake in this statement, since he says, " II doive deja etonner, que les 

 ceufs, la mere changeant de test, ne soient pas considerablement de- 

 ranges, et que la carapace nouvelle, qui les separe du test exterieur 

 de 1' ephippie, ne les emporte pas avec soi ;" but I never said that the 

 eggs were not disturbed ; it requires some practice and much steadiness 

 of hand to remove the old carapace, even from a large specimen, without 

 injuring the animal; but I never said that it could be done without de- 

 ranging the eggs. 



I consider that the external and internal layers of the shell (both of 

 which are formed of epidermis, and are secreted by the corium or chiti- 

 nogenous layer which lies between them), constitute the outer and inner 

 valve of the ephippium, but M. Smitt understands me to suppose that 

 the inner layer of the ephippium is formed by the corium itself; and 

 he adds, that in this case it is impossible to understand in what man- 

 ner the new shell is produced. He suggests, indeed, that as the outer 

 valve of the ephippium is formed of the old shell, so the inner valve 

 may be formed by the new one ; but he admits that this explanation can- 

 not apply to those cases in which the Daphnia survives the removal of 

 the ephippium. 



I must admit that M. Smitt has conclusively disproved the theory 

 which he supposes that I propounded; and I gladly take this opportunity 

 of thanking him for the courteous manner in which he has done so. 

 I trust, however, that, though the relation of the parts is somewhat 

 intricate, the present description is sufficiently precise ; and that, on a 

 second examination, M. Smitt will feel justified in adopting the expla- 

 nation which I have offered. M. Smitt has also made the curious obser- 

 vation, that in Daphnia sima the ephippium contains only one egg. This 

 fact, if it hold good generally, and was not merely the result of accidental 

 circumstances, is certainly very interesting. In D. Schcefferi, which alone 

 I examined with much care, two ephippial eggs were always produced 

 simultaneously, one in each ovary. Since reading IT. Smitt' s paper, I 

 have provided myself with some specimens of D. sima; but have not yet 

 succeeded in meeting with any ephippia. 



Professor Ley dig has observed the male organs in several species. 



