1908] YAMANOUCHI— SPERMATOGENESIS AND OOGENESIS 1O5 



mentioned above, the gamete nuclei, with a few exceptional cases, 

 are of almost equal size at the time of union, and fusion of the chroma- 

 tin of the two gamete nuclei takes place after the dissolution of the 

 portions of the nuclear membranes which are in contact. 



There are described among gymnosperms cases in which there is 

 a marked difference in size between male and female nuclei, as Thuja 

 (Land 58), Picea (Miyake 64), Abies (Miyake 65), Torreya (Rob- 

 ertson 73), Sequoia (Lawson 59), Cryptomeria (Lawson 60). In 

 these species the sperm nucleus, being considerably smaller, becomes 

 imbedded in a depression of the egg nucleus. However, the process 

 of their union does not differ essentially from the cases observed in 

 thallophytes and angiosperms, because the chromatin material of 

 both gamete nuclei in resting condition fuses after the disappearance 

 of the contiguous part of the nuclear membrane. 



According to the accounts given by a number of authors there is 

 still another case : in Larix (Woycicki 99) and Taxodium (Coker 

 18), the gamete nuclei which come into contact do not fuse, but the 

 chromatin contents of both nuclei are kept in distinguishable maternal 

 and paternal groups; while in Pinus (Blackman 8; Chamberlain 

 17; Ferguson 28) and Tsuga (Murrill 68) the chromatin of 

 sperm and egg nuclei remains separate, forming two spirems, and only 

 after their segmentation into chromosomes are the two sets of struc- 

 tures brought together in the first cleavage spindle. In these cases 

 there is never present a resting nucleus including both maternal and 

 paternal chromatin within a common nuclear membrane. 



In the case of Nephrodium, as already described, the sperm which 

 entered into the egg nucleus was observed during a certain period 

 without any visible change, entirely imbedded within the chromatin 

 reticulum of the egg nucleus. The chromatin material which con- 

 stituted the body of the sperm begins to disintegrate, and the final 

 result is a reticular structure similar to that which we have noticed 

 in the nucleus of the spermatid before the formation of the sperm. 

 The reticular structures of both sperm and egg nuclei become 

 anastomosed and mixed together entirely within the membrane of 

 the egg nucleus. The spirem of the first segmentation division is 

 organized from this reticulum as a continuous homogenous structure. 



This process of disintegration of the body of the sperm within the 



