33 



RECENT ADVANCES 



IN THE 



PHYSIOLOGY OF GENERATION, 



OF THE UNIMPREGNATED OVUM.* 



THE observations of Bischoff and other inquirers relative to the structure 

 and anatomical relations of the unimpregnated mammiferous ovum, which 

 have been published since the commencement of 1842, have, for the most 

 part, only confirmed the accuracy of results previously obtained. In a few 

 instances, however, they have served to correct erroneous views or to settle 

 questions which were before disputed. 



It is well known that the ovum, when mature, lies at that part of the 

 Graafian follicle which forms a prominence on the surface of the ovary, and 

 is imbedded in a thickened portion (discus proligerus) of the layer of nu- 

 cleated cells (membrana granulosa of Baer) which lines the follicle. The 

 statement of Dr. Barry that the ovum is retained in this position by a 

 peculiar apparatus, called by him the retinacula, has received no con- 

 firmation. Bischoff'f expressly declares that he has never seen anything 

 resembling such a structure. 



Some recent observations on the intimate structure of the coats of the 

 Graafian follicle will be detailed at page 53. 



The parts composing the ovum are, 1. the external 

 thick transparent tunic, known as the zona pellucida; 

 2. the yolk; and 3. the germinal vesicle with the 

 germinal spot (see fig. 2). The investment of the 

 ovum external to the zona pellucida, which Dr. Barry 

 named tunica granulosa has no existence as a dis- 

 tinct and independent structure. It consists merely 

 of an adhering layer of the cells belonging to the 

 membrana granulosa in which, as has just been 

 stated, the ovum is imbedded. 



The doubt whether the zona pellucida be really a solid, transparent, 



* Book vii. sect. ii. chap. iii. p. 1464 of Mutter's Physiology. 



t Entwickelungs-geschichte der Sfiugethiere und des Menschen. Leipzig, 1842, p. 10. 

 t Ovum of sow, after Barry. 1. Germinal spot; 2. Germinal vesicle; 3. Yolk; 

 4. Zona pellucida ; 5. Tunica granulosa of Dr. Barry ; 6. Adherent granules or cells. 



D 



