402 RECORD OF CURRENT RESEARCHES RELATING TO 



ance of the germinal vesicle, the formation of the first directive 

 corpuscle, and the shrinking of the vitellus at the animal pole are 

 the distinctive phenomena of maturity ; these are always effected 

 before the Graafian follicle is burst. At the moment when the vitellus 

 begins to shrink, a delicate layer is formed from the cortical layer and 

 just below the zona pellucida ; this is the true vitelline membrane, 

 and its formation, just as much as the formation of the directive cor- 

 puscle and the shrinking of the vitellus, is due to the same cause. 

 The rejuvenescence of the cell presents two phases ; in the first the cell 

 frees itself of a definite portion of its nucleus (directive corpuscles), 

 and of certain protoplasmic elements (perivitelline liquid and vitelline 

 membrane) ; in the second phase the expelled bodies are replaced, 

 owing to the conjugation which is effected between the female portion 

 of the ovum and the one or more spermatozoids. 



Like the ovum of all other Vertebrata, that of the Mammalia 

 exhibits a distinct polarity ; one pole is marked by the presence 

 of the germinal vesicle, which gets near the surface of the egg. 

 Several weeks before maturity, between it and the zona pellucida, 

 there is a hyaline protoplasmic plate, very similar to the " couvercle " 

 described in Petromyzon. 



The ova found in any given rabbit vary very considerably in size ; 

 it is not necessary to give all M. van Beneden's measurements, as 

 those of one case afford a sufiicient example — the rabbit which 

 was killed seven days four hours after copulation. In it he found 

 four ellipsoidal ova, of which the major axis measured respect- 

 ively 4, 3-7, 2-8, and 2-8 mm., while the minor axis measured 3-3, 

 3*2, 2 • 2, and 2 • 3 mm. Great differences are also to be observed in 

 the size of the germinal spot, as compared with the whole size of the 

 uterine egg. 



The date of impregnation of all the rabbits which were killed 

 during this investigation was carefully noted, and the time of the 

 first copulation was that which was taken as the starting-point. 

 The abdomen having been opened along the linea alba, the uterus, 

 after removal, was opened from its vaginal extremity, and the 

 incision was always made along the middle line of the face opposite 

 to the insertion of the mcso-peritoneal mesentery. The ova were 

 then carefully removed, and examined either in the fresh state, in 

 a solution of albumen, salt solution, or aqueous humour, and some 

 were measured and drawn before being subjected to the action of 

 any reagent. Of all methods the most successful is perhaps that of 

 treatment with osmic acid and Miiller's fluid ; this causes no altera- 

 tion in the character of the vesicle or of the earliest stages of segmen- 

 tation, and there is no change in the transparency, form, or aspect of 

 the constituent cells. Ova thus treated show no change after preserva- 

 tion for five years in glycerine ; the protoplasm alone takes a slightly 

 yellowish or brown colour, while the zona pellucida becomes bright 

 green, and the albuminous layers remain uncoloured. If the egg is 

 placed directly in Miiller's fiuid, without the intermediation of osuiic 

 acid, it becomes considerably altered. 



Preparations were also made from s])ecimeus treated with nitrate 



