FALLOPIAN TUBE OR OVIDUCT (FUNCTIONS). 



miles is carried with it into the mouth of the 

 Fallopian tube. 



609 



In ova which are not quite ripe, these nu- 

 cleated cells are round, but during the oes- 

 trus, in the riper ova, the cells become elon- 

 gated and fusiform, having their pointed ends 

 attached to the zona pellucida or bounding 

 membrane of the ovum. They present a 

 glassy swollen aspect, by which the fully ripe 



Fig. 410. 



Ripe ovum from the ovary. Guinea-pig. 

 Bischoff.) 



(After 



ova acquire an appearance of being sur- 

 rounded by rays. This change occurs in 

 most mammalia, as the dog, rabbit, sheep, 

 rat, roe, and kangaroo. It is characteristic 

 of the mature ova, and may be regarded as a 

 certain sign of their ripeness. 



Corresponding with this external alteration 

 in the appearance of the ovum, are certain 

 internal changes, of which the chief is the 

 disappearance of the germinal vesicle. This 

 indeed seems to be an almost constant phe- 

 nomenon throughout the mammalia, though, 

 as to the precise mode, or even time, of dis- 

 appearance of this important constituent of 

 the ovum, observers are by no means agreed. 

 By Barry it was considered, after close ob- 

 servation, that the vesicle was not dissolved 

 nor ruptured, as many now suppose, but that 

 it became lost to observation by retiring to 

 the centre of the ovum, where it was changed 

 in character by an internal process of cell de- 

 velopment. 



These changes, external and internal, are 

 the precursors of impregnation, and charac- 

 terise the ovum shortly prior to and at the 

 period of its quitting the ovary. 



Arrived within the Fallopian tube, the first 

 alteration which the ovum experiences is the 

 stripping off of the ray-like appendage of nu- 

 cleated cells with which it quitted the ovary. 

 This change results apparently from a burst- 

 ing and diffluence of these cells, now no 

 longer capable of serving any useful purpose ; 

 Sttpp. 



for the conjecture that they might furnish 

 materials for the construction of the chorion 

 has not been supported by any direct obser- 

 vations. On the contrary, numerous obser- 

 vations of Bischoff show that this process of 

 freeing the ovum from its surrounding layer 

 of cells, takes place very soon after its en- 

 trance within the tube, and generally in the 

 upper third. 



Fig. 411. 



The ovum on first arriving in the Fallopian tube. 

 The ray-like appendages are nearly stripped off. 

 (After Bischoff.) 



a, zona pellucida ; b, granular bodies between the 

 zona pellucida and yelk. Rabbit. 



And now, if the coitus does not obtain, 

 and no contact of the generative elements 

 occurs, the ovum perishes ; observations at 

 least relative to its further fate are wanting. 

 But should the ovum have become fertilised, 

 then a noticeable series of changes takes 

 place, of which the following are the most 

 important. 



The zona pellucida, or transparent bound- 

 ing membrane of the ovum, having been freed 

 of its external granular investment, the entire 

 ovum presents the condition represented in 

 figure 412. Deprived now of all encum- 

 brance, the surface of the ovum is in a 

 condition eminently favourable for the pas- 

 sage through it of the spermatozoa, which 

 penetrate readily that soft outer coat, and 

 thus gain admission to the yelk. 



The fact of the penetration of the outer 

 coat of the ovum by the spermatozoa, which 

 has been so often asserted and denied, may 

 now, after much controversy, be considered 

 as established. In the mammalian ovum, 

 this passage may take place apparently 

 through any portion of the outer coat, j ust 

 as it does in the ova of amphibia, and not 

 through a special pore or microphyle, such 

 as exists in the ova of osseous fishes. 



Following this act of penetration occurs 

 a change which apparetly affords the first 

 distinct evidence that the power of the sper- 

 matozoa has been efficiently exerted upon 

 the ovum. The yelk, which had previously 

 completely filled the zona, is observed to 

 have become contracted, so that an inter- 

 space is left between it and the zona, termed 

 by Newport, who has carefully watched its 

 formation in the ova of amphibia, the " re- 

 spiratory chamber." Such a retiring of the 

 yelk, so as to leave an interspace between 



R K 



