76 THE ITATXJRAL- HISTORY EEA^IEW. 



by passing tlirougli holes in tlie membrane of the oogonium, a mode 

 of access which we have abeady seen to occur in SphcBroplea. 



We must not part with the Zoosporese without mentioning the 

 observations of M. Cohn and Mr. H. J. Carter* on reproduction in 

 the VolvocinesB. Although these two writers are at variance with 

 ref^ard to the monaecious or disecious nature of Volvox globator (the 

 species which has received the greatest amount of attention) there 

 seems no reason to doubt that the sexual process corresponds exactly 

 with that which has been observed in other Alg?e — viz., That it con- 

 sists in the impregnation by spermatozoa of a previously membrane- 

 less "primordial spore." 



In the riorideas the knowledge of the phenomena of impregnation 

 is far less advanced than in the other two divisions. The organs of 

 fructification are of three kinds, 1st, the tetraspores consisting of 

 an oblong or globular external cell enclosing four spores, each of 

 which is capable of 'germination and of reproducing the plant 

 directly ; 2nd, antheridia, containing corpuscles which have been, 

 regarded as spermatozoa, but the nature of which is as yet extremely 

 doubtful. 



It is stated in Mr. Berkeley's Introduction to Cryptogamic 

 Botany, that the plants of this division produce antheridia filled 

 with active spermatozoa ; but although some observations to this 

 eff'ect have been recorded by Derbes and Solier, they have not been 

 confirmed by other botanists. Dr. Pringsheim, at the meeting of 

 German Naturalists at Bonn, in the year 1857 (a report of which 

 is to be found in the Botanische Zeituug for 1857, p. 784), un- 

 hesitatingly denies the existence of spiral or motile filaments. Since 

 that time Dr. Grustav Yenturi has describedf certain organs occurring 

 in Wranaelia penicillatay Polysiphonia elongata, and Callithamnion 

 vesicolor, which have the appearance of being antheridia. He did 

 not, however, find true spermatozoa, although in Callithamnion 

 versicolor the upper cells of the so-called antheridia contained 

 minute cellules in which slight movements were observed, but whicli 

 movements might possibly have been only molecular. 



" Thirdly, besides the tetraspores and the so-called antheridia, the 

 Eloridese produce spores grouped in definite masses, and usually, but 



* See Annales Sc. Nat. 4 Ser., Vol. v. p. 323. Ann. and Mag. of Nat. Hist. 

 Jan. 1859. 



t See " Beobachtungcn liber die Fructifications-organe der Florideen." Wien 

 Z. B. V. Vol. X. p. 583. 



