Miscellaneous. 1 1 S 



This fact was ohservod hy Af?aH«i/. ; hut I have hern ahle to f^o 

 further thiiu that illustrious uaturalist. In fact I have ascertained 

 that tliis (lisappenrauoe of the alhumen is connected Koh'ly with the 

 development of the emltryo and of the vascular lamella, which, in 

 its orifrin, is not distinpfuished from the embryo itself. The allm- 

 men disajipears only above the circle formed by the vascular area ; 

 and its disapju-aranco increases like this circle. If by chance, as 1 

 have observed in my experiments, the vascular area ])resent8 an 

 elliptical form, the em])ty space produced by the disappearance of 

 the albumen presents the form of an elliptical cylinder, or, more 

 correctly, of a ])ortion of a cone with an elliptical base. Thus 

 during the early part of the develoj)ment the formation of the vas- 

 cular area is coiuieoted with the gradual disappearance of the layer 

 of albumeii corresponding to it on the other side of the vitelline 

 membrane. On the contrary, nothing of the kind takes place in all 

 tliat portion of the blastoderm which is beyond the vascular lamella 

 and surrounds it. 



This led me to think that the albumen necessary for the nutrition 

 of the eml)PiO does not assist in the nutrition of the blastoderm 

 itself. I have verified this prevision by the exaraiuation of blas- 

 toderms which had developed without producing any embryo, 

 and which nevertheless had covered almost the whole surface 

 of the yelk. This fact I have several times observed in the 

 course of my teratogenical studies. Under these circumstances the 

 albumen forms a perfectly continuous layer above the blastoderm. 

 We must therefore assume that the blastoderm derives its elements 

 from the yelk, whilst at the commencement of incubation, and, at 

 least, up to the period of the complete closure of the amnios, the 

 embryo is developed at the exjiense of the albumen. 



I may add that the ascertainment of the disappearance of the 

 albumen is the jtrocess that I adopt in my investigations whenever I 

 wish to know whether an embryo is being developed in an egg, a 

 fact which the death and disorganization of the blastoderm do not 

 always allow to be ascertained directly. There arc, in fact, many 

 circumstances under which the embryo perishes very early, quite at 

 the commencement of the development ; and if the o^g is not opened 

 until after the lapse of some days, it is often very difficult to find 

 any appreciable traces of its existence. The disappearance or the 

 preservation of the albumen furnishes a sure means of deciding as to 

 the former existence of an embryo, and to decide whether the 

 blastoderm has produced an embryo or whether it is one of those 

 blastoderms ^nthout an embryo, the occurrence of which in my 

 experiments I have just mentioned. — Comjttes liendiis, Oct. '60, 1870, 

 p. 836. 



On the Stmcttire and Organization of tJie PolyphcmidaB. 

 By l)r. C. Clals. 



The structure of the body and limbs of the Polyphcmida? (Bi/tho- 

 trephts, Pohfphemus, Podon, Evadne) may ho referred in detail to the 



