226 Rickctt.—Fertilization in Sphaerocarpos . 
He observed no receptive spot in the egg. He found that, of many anthero- 
zoids that enter the archegonium, only one penetrates the egg. This at 
once enlarges greatly, and becomes surrounded by a homogeneous hyaline 
area whose outer limit is not well defined. The body of the antherozoid 
then segments, first into four, then into eight threads ; he thought that the 
eight threads result from the longitudinal division of the four seen in the 
earlier stage. The clear area now possesses definite boundaries, which thus 
outline the male nucleus. About the same time, the female nucleus also 
forms eight chromatin threads. The two nuclei become almost equal in 
size. He observed them in contact, but did not see their actual fusion. The 
entrance of an antherozoid causes the appearance of tangential divisions in 
the cells making up the wall of the venter. 
Cavers ( 1904 ), studying Fegatella conica (Conocephalum conicum ), by 
introducing a drop of water full of swarming antherozoids into a prepara¬ 
tion containing mature archegonia was able to follow the opening of the 
archegonium, the extrusion of the mucilage, and the passage of the anthero¬ 
zoid down the neck. He could not distinguish the antherozoid after it had 
penetrated the egg. Large numbers of antherozoids reached the egg and 
caused the latter to exhibit a rocking movement. 
Several stages in the fertilization of Riccia natans (Ricciocarpus natans) 
were observed and figured by Garber ( 1904 ). Numerous antherozoids 
were seen caught in the mucilaginous matter extruded by the archegonium. 
The egg is concave at the end nearest the neck, and, after the archegonium 
has opened, is somewhat shrunken away from the walls of the venter, 
though not nearly so much so as is usually described for Riccia. The 
fertilized egg swells and its end extends up into the neck canal. Garber 
saw the two sexual nuclei lying in the egg cytoplasm. The male is about 
half the size of the female nucleus, and stains more darkly because its 
chromatic contents are more closely crowded together. These contents 
include one or several large bodies and some smaller granules. The female 
nucleus contains a large body in the centre, and apparently a fine reticulum 
surrounding this. There are conspicuous plastids with starch grains all 
through the egg cytoplasm. According to his account, the male nucleus 
approaches the female nucleus and becomes embedded in it, but it is a ques¬ 
tion whether his figures really prove this point. In the absence of state¬ 
ments as to the thickness of his sections, or as to whether the two nuclei were 
at the same focal level, the nuclei may equally well be interpreted as being 
one above the other, no fusion occurring at this stage. As in Riella , the 
entrance of the antherozoid is followed by divisions in the cells of the venter, 
so that the latter consists of two layers of cells before the first division of the 
zygote. 
Humphrey ( 1906 ) saw one stage in the fertilization of Fossombronia 
longiseta , which is noteworthy as being markedly different from anything 
