Dcsmidiece.'] infusortal animaicules. 279 



"M. Morron contoiuls that a sporang-iiim becomes converted into 

 a single frond, and gives a scries of figures in illustration of the 

 changes -which the sporangium undergoes until it becomes " a Clos- 

 termm of two unequal cones." (P. 18, figs. IG, 17, 18, 19.) Now 

 as this form is the result of the self-division of the ordinary frond, 

 and invariably precedes conjugation, I am disposed to think M. 

 Morren has mistaken fronds thus divided, and aftci-wards thrown out 

 of their relative positions, for modified sporangia. 



Self- division, in the case before us, seems only to accompany con- 

 jugation, and ^vill not, as in the other Desmidiem, accoimt for the 

 existence at certain periods of vast multitudes of the fronds 



" I may remark, that in a generic arrangement, based upon the 

 reproductive organs, Clostermn Ehrcnhergii will stand apart fi'om all 

 the other Desmidiece. In it alone a pair of conjugating fronds pro- 

 duce two sporangia. It is, however, allied to others of the present 

 genus thi'ough C. lincatum, the sporangiimi of wliich, according to 

 Mr. Ealfs, is binate, and shows a disjiosition to separate into two 

 parts." 



"Another mode of increase, analagous to the propagation of 

 Zoospores in Algag, has been assigned to the Besmidiem, and it has 

 been alleged that the endochrome escapes in the form of zoospores, 

 and becomes transferred into new fi'onds. M. Morren not only 

 affirms this to be the case, but gives a figure illustrative of the 

 conversion of these zoospores, or as he terms them ' propagules,' into 

 new fronds." (P. 18, f. 15 ) 



Mr. Ealfs states, that " As there is no constriction in Closterium, 

 the process of division is less evident. It is best seen in the striated 

 species, in which the central suture is most distinct. The transverse 

 line becomes double, and, by the iutermediate growth, the frond at 

 length, consists of three portions, as the newly-formed central one 

 continues to elongate, another transverse Kne becomes visible at its 

 middle where a complete separation at length takes place. At first, 

 however, the new segment is often merely a rounded protuberance, 

 and the fi-ond is consequently unequal ; and when it is perfected, 

 if the covering is a coloui'ed one, the newer segment can still be dis- 

 tinguished by its greater paleness. 



" The striated species, besides the central suttu-e, frequently have 



