412 BULLETIN OF THE 



granular substance (nucleoplasma) in the germinative vesicle, in addition 

 to the nucleolus and a clear liquid. The granular substance often as- 

 sumes the form of a network in the growing egg. At maturity the 

 vesicle, instead of being central, becomes superficial, takes an ellipsoidal 

 form, and then becomes more and more flattened against the zona pellu- 

 cida. The vitellus is now composed of a medullary mass, and a cortical 

 layer which becomes clear at the contact of the vesicle. Clear proto- 

 plasm is accumulated around the vesicle in the form of a biconvex 

 lens, — la lentille cicatricidaire, — which depresses the medulla. As 

 soon as the germinative vesicle comes in contact with the zona, the 

 nucleolus joins the membrane of the vesicle, against which it is flattened 

 and with which it unites ; its plastic substance spreads out into a plate 

 with, at first, a median thickening, — plaque nudeolaire. 



At the same time the membrane of the vesicle thins out, especially 

 where it is in contact with the cicatricular protoplasm. It is probable 

 that the substance of the membrane is attracted toward, and unites 

 with, the nucleolar plate. The nucleoplasm and pseudo-nucleoli give 

 rise to a mass of granular substance, — corps nucleoiAasmique. The 

 liquid and limpid contents of the vesicle mixes with the cicatricular 

 protoplasm upon the rupture of the membrane of the germinative vesi- 

 cle. At the same time the nucleolar plate, by virtue of its inherent 

 contractility, is amassed into a body having sometimes the form of an 

 ellipsoid, often that of a lens, or of a calotte, — corps nudeolaire. At 

 the moment the germinative vesicle disappears, the directive bodies are 

 eliminated. There are two of these, but they are unlike both in compo- 

 sition and signification ; one is the nucleolar body, the other the nucleo- 

 plasmic body. The former is stained in picrocarminate of ammonia, 

 the latter is not. The cicatricular lens becomes granular, and thus 

 indistinguishable from the cortical layer of the yolk. With the disap- 

 pearance of the germinative vesicle begins the retraction of the vitellus, 

 which consists in the expulsion of a transparent liquide perivitellin, and 

 is accompanied by amoeboid movements. Subsequently the vitellus 

 resumes its spherical form, and no division into cortex and medulla is 

 visible. In this cytode state the egg is entitled to Haeckel's designa- 

 tion, " monerula." All the preceding changes are independent of fecun- 

 dation, and are connected with the maturation of the ovum. In the 

 case of the rabbit they are accomplished within the ovary. 



Although a portion of what is said in his chapter on the " Formation 

 of the first Embryonic Nucleus " pertains to another part of the present 

 review, I shall give it in this connection. Shortly after fecundation 



