336 REPRODUCTION IX 



beak at one end, and which from their extreme resemblance to ani- 

 malcules and their lively movements are called Zoospores. And 

 these zoospores germinate by elongation and the formation of trans- 

 verse partitions into adult thread-like plants, consisting of a row of 

 cells. The whole contents of the cells of some adult individuals of 

 Sphajroplea are formed into large green spores, as yet without a coat ; 

 those of different individuals give rise to myriads of slender sperma- 

 tozoids, moving by means of a pair of cilia fixed at the narrow end. 

 These escape from the parent cell through a small perforation which 

 now appears, enter the spore-bearing cells of the fertile plant 

 through a similar perforation, play around the spores, and at length 

 one or more of them drives its pointed extremity into their naked 

 surface ; after which, fertilization being accomplished, a thick coat 

 of cellulose is deposited to complete the spore. 



GG1. That in the Fucaeea? or olive-green Seaweeds, the highest 

 tribe of Alga;, the large spores are fecundated by spermatozoids, or 

 minute lively-moving cells produced in antheridia, was demonstrated 

 by Thuret in the year 1850.* And in more recent memoirs f he 

 has shown that the fertilization takes place through direct contact of 

 the spermatozoids with the naked surface of the unimpregnated spore, 

 then having only a protoplasmic coating ; and that these spores will 

 not develop unless so fertilized. Through the researches of Thuret 

 and others, antheridia are now well known in the remaining or 

 rose-red series of Alga?, although their spermatozoids are not known 

 to be endowed with motivity. The same appears to be the case with 

 Lichens, the bodies described by Itsigsohn,J being probably of the 

 nature of spermatozoids or fertilizing cells. In the vast family of 

 Fungi there are similar indications of antheridia and spermatozoids, 

 but the fecundation is not yet clearly made out. 



G62. Fertilization by Spermatozoids of a Cell in a Pis'.ilidium, which 

 becomes a Sporangium. In all the foregoing cases, the spores them- 

 selves are the subjects of direct fertilization. But in Mosses,' 

 Liverworts, &c. (in which the two kinds of organs have long been 

 recognized and their functions to some extent understood), the 

 contents of the antheridium act upon an organ which, in conse- 



* Ann. Sci. Nut. scr. 3, vol. 14 ami 16, 1850-1. See Harvey, Nereis Bor.- 

 Atner. in Smithsonian Contributions, 1852, &c. 

 t Op. cit ser 4, vol. 2 and 3, 1854, 1855. 

 J In Botamsche Z.itumj, 1850. 



