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CHAPTER XL. 



IMPREGNATION OF THE OVUM. CHANGES IN THE OVUM IMMEDIATELY 

 SUCCEEDING IMPREGNATION. ROTATION OF THE YOLK. CLEAVAGE 



OF THE YOLK. KOLLIKER's OBSERVATIONS. FORMATION OF 



BLASTO-DERMIC VESICLE, OR GERMINAL MEMBRANE. FORMATION 



OF DECIDUA. STRUCTURE OF THE MEMBRANA DECIDUA. 



DECIDUA REFLEXA. 



Impregnation of the Ovum. It is exceedingly difficult to give a 

 satisfactory description of the nature of the phenomena occurring 

 in impregnation. It was recently held, by Mr. Newport and 

 other observers, that the contact of the spermatozoa with the 

 exterior of the ovum was sufficient to impregnate it. It was 

 supposed, that liquefaction of the spermatozoa occurred, and 

 that the solution thus formed permeated the vitelline membrane, 

 and impregnated the ovum. The latest researches, however, of 

 the same indefatigable investigator upon the ovum of amphibia, 

 and upon the mammalian ovum, have demonstrated satisfactorily 

 that the spermatozoa actually penetrate and pass through the yolk 

 membrane, and are thus brought into contact with the yolk in the 

 interior. This view was advocated by Dr. Barry several years ago 

 (in 1843), and its accuracy has since been confirmed by the obser- 

 vations of Newport and Bischoff, and also by Meissner. 



What becomes of the spermatozoa when they have reached the 

 interior is unknown. They disappear, and become liquefied ; but the 

 precise manner in which this occurs has not been determined, neither 

 is it known if they penetrate far into the substance of the yolk. 



Micropyle. In many ova the vitelline membrane is very firm 

 and hard; and it may be fairly asked, how can the delicate sper- 

 matozoa perforate so tough a structure as the investing membrane 

 of the yolk undoubtedly is in these ova? Much light has very 

 lately been thrown upon this part of the process of impregnation 

 by the researches of our friend, Dr. Hansom, of Nottingham, by 

 those of Professors Miiller and Eemak upon the impregnation of 

 the ova in fishes, and by the investigations of Leuckart, Leydig, 

 and Meissner, upon the eggs of insects, mollusks, and some of the 

 radiata. 



VOL. n. p P 



