310 On the Theory of the Fecundation of the Ovum, 



of the albumen. This however appears to be of but little 

 importance, as it is very possible that this membrane may some- 

 times be present and sometimes absent. It is only necessary 

 to suppose, that where it occurs it is pierced by a second micro- 

 pyle, or that the spermatozoa can pass through its tissue. A 

 more important point, in our opinion, is the complicated struc- 

 ture presented by the membrane of the micropyle in the Fishes, 

 the HolothuricE, the Insects*, and probably other animals; for 

 there are many ova in which the micropyle has not yet been 

 discovered, but in which the external membrane presents a 

 shagreened structure, resembling that of the membrane of the 

 micropyle in Fishes. This is the case, for example, in the ova of 

 the Echinorhynchi, &c. But this complicated structure is an 

 obstacle to the theory of Meissner upon the formation of the 

 ova, of much greater force than all the objections which Bischoff 

 was able to bring against it. Is it possible to regard a whole so 

 complex as this membrane as a simple cell ? There can be no 

 doubt that we must reply in the negative. We must therefore 

 either reject the observations of Meissner upon the formation of 

 the ova of Mermis, or, as they have such an impress of truth 

 that it is difficult not to yield to them, admit that the ovum is 

 formed in very different modes in the series of created beings. 

 The latter opinion has nothing improbable about itf. 



The penetration of the spermatozoa into the ovum is a fact 

 now acquired to science ; but this penetration may take place in 

 very different manners, and we can already distinguish three 

 principal types : — 



1. Penetration through a micropyle; a mode of fecundation 

 which appears to be very widely spread, as its existence has 

 already been ascertained in Echinodermata, Worms, Insects, 

 Crustacea and Fishes, and perhaps also in Reptiles (Hyla) and 

 Mammalia (the Rabbit). 



2. Penetration by all points of the surface of the ovum; 

 observed by Newport in the true Frogs. It is true that we may 

 in this case suspect an error, and that it is possible that a micro- 

 pyle may some day be discovered in the Frogs ; but is it not 

 surprising that such careful researches as those which have been 



* It is probable, however, that it is not in the external membrane of the. 

 eggs of Insects that we find the analogue of the membrane of the micro- 

 pyle in other animals. It is probably rather the inner membrane, which is 

 also traversed by the micropyle. Leuckart however believes he has seen 

 instances in which the chorion (or outer membrane) alone was traversed by 

 the micropyle. 



t More especially as Lov^n and Leuckart have shown that the ova are 

 formed in a very different manner in Modiolaria, Cardium, and the Naiades, 

 The multiple micropyle of the eggs of the Hemiptera and Lepidoptera also 

 indicates a very different mode of formation. 



