GENERATION. 



515 



of things will be shown to originate in the periodical alternation of gen- 

 eration and gemmation respectively. 



1ST. OP GENERATION. 



Eeproduction by generation is accomplished on two different types : 

 1st. By the conjugation of two similar cells ; 2d. By filaments. 



In the first, that is, by the conjugation of two similar cells, a third 

 body, called a sporangium, results. Of this process there Three modifi 

 appear to be three different modifications : 1st. The two sim- cations of con- 

 ilar conjugating cells discharge their endochrome, or coloring J u s atlon - 

 material, each voiding itself completely, and the sporangium arises from 

 the mixture ; 2d. A dilatation forms on the point of union of the two 

 conjugating cells, and into this dilatation the endochromes of both cells 

 are passed ; 3d. The endochrome of one cell is wholly retained, and that 

 of the other is added to it, the one becoming void, and in the other the 

 sporangium being produced. This, occurring in the lowest vegetables, 

 among which it was for a long time supposed that the type of reproduc- 

 tion is totally different from that of flowering plants and animals, pre- 

 sents us with the first traces of what is eventually displayed as differ- 

 ence of sex. 



This shadowing forth of the difference of sexes is illustrated in a very 

 instructive manner by the Zygnema quininum, a fresh-water conferva. 

 Its manner of growth is what has been already described in the case of 

 the Conferva glomerata, Fig. 231. In the annexed Fig. 245 is repre- 



. Development and reproduction of Zygnema quininum. 



sented at A the process of growth by the subdivision of cells, a b c repre- 

 senting three such cells, the middle one, 5, being in the act of subdivision. 

 At B two threads are in the act of conjugation. The endochromes of 

 both are spirally arranged, and dilatations reaching from one to the other 

 are here and there seen. At C the endochromes of one thread, <z, have 

 wholly passed over to the other thread, b, and the round bodies, or spo- 



