462 



GENERATION. 



productive power is given to the egg, but to 

 endeavour to establish what are the essential 

 conditions of fecundation. 



Difference between the fecundated and unfe- 

 cundated ovum. In the first place, in reference 

 to this subject, it would be interesting to know 

 whether any material difference exists between 

 the structure of the fecundated and unfecun- 

 dated egg. 



In the common fowl we have seen that the 

 whole substance of the egg, the yolk and ger- 

 minal portion, the albumen, shell, and mem- 

 brane, may be formed in the ovaries and oviduct, 

 and excreted from the body of the hen without 

 any connection with the cock ; but such an 

 egg, though apparently the same in structure 

 with that which is laid after connection with 

 the cock, when subjected to the requisite heat, 

 undergoes none of the changes of development 

 which incubation induces in the fecundated 

 egg, but only passes into chemical decomposi- 

 tion like any other dead animal substance. 



Did any difference of structure exist between 

 the fecundated and unfecundated egg, we 

 should be disposed to look for it first in that 

 part of the egg which is more immediately con- 

 nected with the new being, viz. in its germinal 

 portion ; but we regret to say that the investiga- 

 tions of naturalists have not as yet pointed out 

 any marked difference in a satisfactory manner. 

 Malpighi, it is true, long ago pointed out a 

 difference in the structure of the cicatricula of 

 the egg of the common fowl which had had 

 connection with the cock, and those of the hen 

 living single, and the observations of this author 

 were afterwards confirmed by Prevost and 

 Dumas. In the impregnated egg the cicatri- 

 cula is a well-defined whitish spot, with a re- 

 gularly formed transparent area in its centre ; 

 while in the unimpregnated egg there is no re- 

 gularly shaped transparent area, but rather a 

 number of small irregular clear spaces scattered 

 over the surface of the cicatricula. We fear, 

 however, that this appearance of irregularity 

 exists as well in some eggs that have been laid 

 after connection with the cock, and that the 

 shape or appearance of the cicatricula can 

 scarcely be depended upon as informing us 

 whether an egg has been fecundated or not, 

 since that appearance is much influenced by 

 the state of the nucleus or white matter of the 

 yolk situated below it, as well as by the state 

 of the cicatricula itself. This subject is worthy, 

 however, of the most accurate investigation, as 

 it appears to offer the prospect of affording 

 some information on this very obscure part of 

 the generative process. 



In the ovarian ovulum, the vesicle of Pur- 

 kinje, it will be recollected, occupies the centre 

 of the cicatricula; and this vesicle exists in the 

 ovulum so long as it remains within the ovarian 

 capsule, whether the hen have connection with 

 the cock or not. In the impregnated fowl the 

 germinal vesicle of Purkinje bursts, and leaves 

 the transparent area in the centre of the cicatri- 

 cula at the time when the ovulum passes from 

 the ovarian capsule into the oviduct ; but it re- 

 mains to be known if the same is the case, or 



what phenomena ensue upon the escape of the 

 ovulum from the ovarium in the fowl which is 

 entirely separated from the cock.* 



We do not know with certainty what befalls 

 the vesicle of Purkinje in the ovulum of Mam- 

 malia at the time of its escape from the ovarium. 

 The analogy of all oviparous animals is strongly 

 in favour of the supposition that it bursts in the 

 same manner. M. Coste states that it does not 

 burst, and Valentin supports an opposite view. 

 While, therefore, we feel disposed to adopt 

 the opinion that the seminal fluid, in fecunda- 

 ting the egg, operates its peculiar change chiefly 

 on the germinal part, and that the bursting of 

 the germinal vesicle is very probably connected 

 with the change of fecundation, it must be ad- 

 mitted that further observations are still want- 

 ing to afford a satisfactory proof of the correct- 

 ness of these hypotheses. 



Is material contact of the semen and ovum 

 necessary for fecundation'? No one has ever 

 discovered any of the seminal fluid within the 

 egg : the most minute observation does not de- 

 tect any appearance of this. A question then 

 naturally presents itself in reference to the sub- 

 ject of our present inquiry, viz. whether it is 

 necessary that a certain quantity of the sub- 

 stance of the seminal fluid should be brought 

 into actual contact with the egg in order to 

 cause its fecundation 1 and if so, in what man- 

 ner and in what part of the female organs such 

 contact is brought about? 



Were we to look no further than to the 

 manner in which fecundation is effected in 

 many of the inferior animals, we might be in- 

 duced at once to form the opinion that the mere 

 contact of a certain quantity of the seminal fluid 

 with their ova, in whatever way brought about, 

 is all that is necessary for producing their fecun- 

 dation. Thus, in the greater number of fishes 

 the milt or seminal fluid of the male is shed 

 over the spawn of the female after it is laid in 

 water, without there being any nearer sexual 

 intercourse; the fecundation is external to the 

 body of the female, and we thus know with 

 certainty that the ova and the seminal fluid are 

 the only parts immediately concerned in the 

 process. The same is the case in the common 

 frog, in which there is copulation ; for in that 

 animal, although the male and female remain 

 united firmly together during a longer period 

 than any other kind of animal, yet this union 

 is not a means of producing fecundation, but 

 rather of promoting the discharge of unim- 

 pregnated ova from the generative system of 

 the female. There is in fact no true sexual 

 union : the spawn is laid by the female un- 

 fecundated, and the male (separating then in 

 general from the female) sprinkles seminal fluid 

 on the ova floating in water. 



External and artificial fecundation. The 

 mode of fecundation just now mentioned sug- 



* We have long had the intention of instituting 

 a series of observations comparing the changes of 

 the impregnated and unimpregnated ovum in the 

 oviduct, but have not vet had an opportunity, and 

 we recommend it to those who may be anxious to 

 engage in the investigation of this subject. 



