342 Mr. Hassall's Notices of British Freshwater Conferva, 



when they present a small transparent prolongation, either 

 straight or slightly curved, do not move it at all ; but it hap- 

 pens that, following the side by which they present them- 

 selves to the eyes of the observer, this prolongation is visible 

 or it is not. It is necessary, in order to perceive it, that the 

 corpuscles be in profile ; in that position it is easy to assure 

 oneself that the prolongation or beak does not make any 

 movement." 



My own observations, so far as the freshwater Conferva? 

 with simple unbranched filaments are concerned, accord en- 

 tirely with those of M. Decaisne ; but in another class of Con- 

 fervas, upon which I hope shortly to prepare some observa- 

 tions, I have without doubt frequently seen the perforated 

 papilla, as well as, I believe, though not satisfactorily, the re- 

 markable motion of the zoospores. 



M. Decaisne, in the memoir already alluded to, likewise 

 combats the opinion entertained by Agardh, of the existence 

 of two forms of reproductive bodies in some of the genera 

 composing the class (now fast losing its former importance) 

 of Zoospores, for the one of which the term zoospore is espe- 

 cially reserved ; this being the small rostrated body endowed 

 with a lively motion, of which many, according to Agardh and 

 M. Decaisne, may be contained in a single cell of Confervae ; 

 and the other the much larger spheroidal or elliptical body, 

 resulting often, as in the Conjugate, from a union and con- 

 centration of the contents of two distinct cells. " If, as it is 

 advanced," observes M. Decaisne, "the zoospores and the 

 spherical globules develope themselves in the same manner 

 by the production of filaments, by their growth or extension, 

 it is evident that they present, at a determinate period of their 

 life, specific characters perfectly distinct, for the tubes pro- 

 ceeding from the spores should have a calibre much more con- 

 siderable than those furnished by the zoospores. It appears 

 to me, therefore, impossible that the same plant can give birth 

 by its germination to two beings specifically different, if it is 

 admitted in all cases that the length and diameter of the cells 

 present, for each particular species, characters constant at a 

 given period. Moreover, it is necessary to suppose that the 

 filaments proceeding from the zoospores enjoy a power of de- 

 velopment much greater than the others, to attain in one day 

 the same diameter. The physiologists who have admitted this 

 double mode of reproduction are in general contented to say 

 that the zoospores develope themselves into filaments like to 

 the parent plant ; but this has not been, that I am aware, 

 represented in any of their works ; while, on the contrary, we 

 there find described and figured in detail the series of deve- 



