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 archegoniwm is usually directed 
forwards towards the notch of the prothalliwm, 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 imp ET 
tb 
understood, however, or the impregnation (it being 
sie that this happens under such circumstances that the spermatozoid 
is from the antheridium, and the mucilage of the canal of the archegoniwm 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 
a. the a In the earliest state that I have been able to see clearly, a little 
»e ot minute cellular structure occupied the place of the embryonal vesicle (figs. 71, 75), 
* It is unimportant which we call it 
à » Since it is here developed at i | 
the germinal vesicle usually be ivi pec. at once into the embryo. In flowering plants 
embryonal vesicle, y Decomes subdivided to form a suspensor, and one of the cells produced by it becomes the 
