Osmunda claytoniana , Z., and O. cinnamomea , L. 71 
the spermatozoid, the prothallia were treated as in studying 
the development of the spermatozoids. As the entrance of 
the spermatozoid can be seen, it is only necessary to allow 
them to enter, and then, after waiting as long as may be 
desired, to plunge the specimen into the fixing fluid. On 
examining specimens so treated it is found that the nucleus of 
the egg moves toward the receptive spot at the time of fertili- 
zation, and that the spermatozoid, immediately after its 
entrance, has undergone but little change (Fig. 76). The 
spermatozoid, almost at once, comes into contact with the 
female nucleus, and with it moves toward the centre of the 
egg. Here the spermatozoid gradually loses its coiled form, 
contracting until it forms an oblong nucleus, in close contact, 
apparently, with the female nucleus, although it was not 
always easy to tell whether it was simply in contact with it, 
or actually within. The process is a slow one, as in one case, 
twenty-four hours after the entrance of the spermatozoids the 
two nuclei were still distinguishable (Fig. 78). Finally, the 
two nuclei are completely fused, and a single nucleus is seen, 
sometimes larger than the nucleus of the unfertilized egg, and 
containing usually, if not always, two nucleoli (Fig. 79). The 
fertilized egg is now surrounded by a membrane that probably 
begins to form almost immediately on the entrance of the first 
spermatozoid, and prevents the penetration of others. This 
seems probably from the fact that although numerous sper- 
matozoids often penetrate to the central cell (Fig. 74), only 
one, so far as observed, ever enters it. No sign of a separation 
of the nuclear segments of the copulating nuclei was seen. 
Although numerous sections of the freshly fertilized egg were 
made, I was not fortunate enough to find any in which the 
nucleus was undergoing division. 
As the archegonium matures, a single layer of narrow cells 
is formed around the central cell. These are especially dis- 
tinct when the archegonium is cut transversely. After fertili- 
zation these cells begin to divide actively in all directions. 
Their contents show more abundant protoplasm and larger 
nuclei, and, indeed, all the evidences of actively growing cells. 
