126 MR. HENFREY ON THE DEVELOPMENT 



necessary stimulus. I imagine this stimulus resides in the mucilaginous fluid in which 

 the spermatozoid is bathed in the sperm-cell, and which, adhering to this, is conveyed to 

 the mucilage (protoplasm) of the germinal vesicle, just as the contents of the pollen-grain 

 become combined with the protoplasm of the germinal vesicle in flowering plants. The 

 nature of the process is clearly a problem beyond the reach of science, but it seems to be 

 a necessary induction, from the facts in the Phanerogamia, that the phenomena result 

 there from the material union of two fluids, and I hence conclude that this is the case 

 here. The comparatively few cases of successful impregnation among these prothallia, so 

 many of which prove sterile, may perhaps be accounted for by the peculiar conjunction of 

 circumstances required to bring a sufficient amount of the fertilizing fluid, by means of 

 the spermatozoids, to the germinal vesicle, at the precise epoch required. 



Some doubt has been thrown upon the possibility of the impregnation of the archegonia 

 by means of the spermatozoids, on the ground that the free movement of the latter in the 

 water, beneath the microscope, is an abnormal condition. I attach no weight to these 

 objections, for the occurrence of numerous empty antheridia, on moderately developed 

 prothallia, proves that their dehiscence is a natural process, and if the moisture which 

 always exists upon the under surface of the prothallia is insufficient to allow such a wide 

 and free course to the spermatozoids as they find in the water on the glass slider beneath 

 the microscope, we see a compensation for the obstacles in the way of the conjunction in 

 the large number of antheridia produced, and this not at one time only, but throughout 

 the whole growth of the prothallium. Again, there is evidence that the process is not 

 easily and constantly completed, in the fact of so many prothallia remaining sterile, and 

 in the provision of several archegonia upon each, while in normal cases only one produces 

 an embryo. 



Arguments have been urged against the entrance of the spermatozoids into the archego- 

 nium, from the consideration that the mouth of the canal is directed downwards, and the 

 spermatozoid would consequently have to work its way upwards, contrary to the attraction 

 of gravity ; and further, from the fact that the apex of the archegonium is usually directed 

 forwards towards the notch of the prothallium, while the antheridia occur principally about 

 the posterior part. If we imagine the contact of "the spermatozoids with the mucilaginous 

 matter protruding from the mouth of the canal to suffice for the impregnation (it being 

 understood, however, that this happens under such circumstances that the spermatozoid 

 is fresh from the antheridium, and the mucilage of the canal of the archegonium has not 

 yet become coagulated by exposure), this difficulty is done away. 



The first result of the impregnation, — that is to say, the first step of development of the 

 embryo, which I believe to be the consequence of such an operation, — as seen by means 

 of vertical sections of the prothallium, consists of subdivision of the germinal or embryonal 

 vesicle* of the archegonium. In the earliest state that I have been able to see clearly, a little 

 globe of minute cellular structure occupied the place of the embryonal vesicle (figs. 71, 75), 



* It is unimportant which we call it, since it is here developed at once into the embryo. In flowering plants 

 the germinal vesicle usually becomes subdivided to form a suspensor, and one of the cells produced by it becomes the 

 embryonal vesicle. 



