8U PROGRESS OF MICROSCOPICAL SCIENCE. 



Barry's observation has been confirmed by a great number of embryo- 

 logists, amongst whom we may mention Bischoff, Lehmann, and 

 Meissner. Spermatozoa have been found by those observers in 

 the albuminous envelopment of the ovum of different mammals, 

 during its passage through the oviduct, farther in the zona pellucida, 

 and between the latter and the germ (yolk) itself. They have 

 been seen in the latter place, not only previously to the cleavage 

 process — when the germ (yolk) had retracted itself from the zona 

 pellucida — but also in a later period, when the germ was already 

 divided into a number of cleavage globules. In all these instances, 

 however, the spermatozoa were motionless. Dr. Weil has observed in 

 a number of ova, taken from the oviduct between the 17th and 46th 

 hours after fecundation, spermatozoa in very lively movement in the 

 albuminous envelopment as well as within the zona pellucida. Weil 

 gives an account of four instances where he has seen unchanged sper- 

 matozoa in the substance of the germ itself, besides numbers of moving 

 spermatozoa between the germ and the zona pellucida. There were 

 to be found in these and other instances filaments either isolated or in 

 bundles inside the germ, which Weil regards as the tails of spermato- 

 zoa. In later periods, when the ovum had already reached the uterus, 

 no spermatozoa were to be found, neither outside nor inside the germ. 

 From these facts, Weil takes it as probable that the spermatozoa, 

 after having penetrated the germ, vanish completely, and that this 

 intimate union of the spermatozoa with the germ forms the most 

 material part of the fertilization of the ovum. Consequently, the in- 

 heritance of faculties from the father may be in this way explained. 

 Weil confirms the assertion of Bischoff that the coitus in rabbits is 

 not to be regarded as the chief cause of the extrusion of the ova from 

 the ovary ; but that, if there exist a relation between the coitus and 

 the extrusion of the ova, it is only in so far as the former takes place 

 a few hours before or after the latter. According to Weil, each ovum 

 possesses two vesicular nuclei before the cleavage process commences. 

 As to the earliest changes of the ova on their way through the oviduct, 

 Dr. Weil's observations confirm those of Bischoff, fully described in 

 his great work on the development of the rabbit's ovum (1842), which 

 may be briefly described as follows : — The germ is first closely sur- 

 rounded by the zona pellucida ; then the germ retracts itself from 

 that membrane; farther, the germ divides itself into two halves, each 

 of these again into two halves ; then the germ consists of eight 

 cleavage globules, and finally of sixteem In ova taken from the 

 uterus (four days), the germ is already transformed into a vesicle 

 (vesicule blastoclermique of Coste), which exhibits on its surface a 

 mosaic of cells, and on one place a mass of opaque elements, pro- 

 jecting into the cavity of the vesicle. In a later stage (five days), 

 this vesicle consists only of one layer of cells ; that is to say, the 

 elements which result from the cleavage of the germ have arranged 

 themselves in one layer, which encloses the cavity of the vesicle. In 

 a still later stage (seven days), the vesicle shows a circular opaque 

 spot, which consists of two layers of cells, whereas all other parts of 

 the vesicle have only one layer. Not being able to find the above- 



