. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 610 UTERUS AND ITS APPENDAGES. the latter and the zona pellucida, which in- terspace is filled by a transparent fluid, has been noticed in many mammalia, as the Guinea-pig, rabbit, &c. riff. The ovum a little more advanced in the tube. (After Bischoff.) The surface is perfectly smooth. Spermatozoa have penetrated the zona pellucida. The respira- tory chamber is formed between the latter and the yelk. The rotation of the yelk has commenced, as indicated by the arrows. The granular bodies ap- pear preparatory to
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 610 UTERUS AND ITS APPENDAGES. the latter and the zona pellucida, which in- terspace is filled by a transparent fluid, has been noticed in many mammalia, as the Guinea-pig, rabbit, &c. riff. The ovum a little more advanced in the tube. (After Bischoff.) The surface is perfectly smooth. Spermatozoa have penetrated the zona pellucida. The respira- tory chamber is formed between the latter and the yelk. The rotation of the yelk has commenced, as indicated by the arrows. The granular bodies ap- pear preparatory to the segmentation of the yelk. Several of these stages are seen commencing in the preceding figure. Rabbit. This change is preliminary to another oc- currence, which has been observed in the ova of many animals, both vertebrate and invertebrate, viz. the rotation of the yelk within the interspace just described ;— a ro- tation which is effected by the aid of cilia clothing the surface of the yelk. About this time may be observed one, or perhaps two, small granular bodies, whose formation has given rise to many and varied speculations regarding their signification and use. They occupy a portion of the space between the yelk and zona pellucida, and appear to be common to the mammalian ovum and that of other classes. The most probable supposition regarding their use con- nects them with the division or cleavage of the yelk which follows their appearance. Whatever doubts may be entertained as to the dependence of the phenomena already described upon a preceding act of impregna- tion, all question is set at rest at this point, by the direct experiments of Newport, who Fig. 413. ascertained beyond doubt, that segmentation of the yelk is the result of impregnation alone, and that it never takes place in the unini- pregnated ovum. This segmentation of the yelk consists in a spontaneous cleavage of that body, at first into two, and then into four, equal parts; the process of division
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