174 BIOLOGY: GENERAL AND MEDICAL 



cases there are such constant differences between the con- 

 joining cells that it is possible to separate them into male 

 and female elements, or gametes. The development of 

 sexual differences may or may not be incompatible with 

 the continuance of reproduction by fission, though in 

 general it marks the end of the asexual, or monogenetic, 

 and the beginning of the sexual, or digenetic, mode of re- 

 production. 



As in the most simple forms of life, there are no visible, 

 and probably no theoretical differences between the 

 occasionally conjoining cells, so we find that among the 

 primitive forms in which conjugation is constant, and 

 special cells are generated for the purpose, the relation 

 of these cells to one another is so close that they not in- 

 frequently descend from the same parent cell. Thus 

 a spore of the malarial parasite having attained maturity, 

 divides into a considerable number of spores which 

 develop and again divide until eventually through this 

 asexual mode of reproduction a great number of the 

 parasites is produced, all the progeny of a single cell. 

 By and by, however, a time comes when the mature 

 cells cease to sporulate as usual, and develop into mature 

 sexual forms, gametes, with which further development 

 rarely occurs unless conjugation be permitted. 



If, in this case, it should be argued that there is no 

 certainty that the conjoining male and female elements 

 are derived from the same parent because the patient 

 may have a multiple infection, examples taken from the 

 primitive vegetable world may be given to prove the 

 case. 



In the reproduction of Eurotium repens both the 

 asexual and sexual methods may be observed. The 

 former, which is accomplished through spores, may be 

 looked upon as a kind of fission; the latter, after a definite 

 conjugation, results in the formation of a peculiar peri- 

 threcium in which a smaller number of ascospores is 

 developed. The formation of the perithrecia is not 

 easy to follow. As described by de Bary, " they begin 

 in the form of tender branches which at the termination 



