368 DESMIDE^. 



of which is occupied by a vesicle filled with active mole- 

 cules. 



Derivation. From Kkcoar'qp, a fine thread ; in allusion to 

 the attenuated form of the frond. 



The two peculiarities which distinguish the genus Clos- 

 terium from all other DesmidecB are the crescentic form of 

 the fronds and the i^resence in the free extremity of each 

 of the segments, of the vesicle filled with revolving particles. 

 These i}articles occasionallj escape from the vesicle, and cir- 

 culate vaguely and irregularly round the circumference of 

 the frond. The use of these particles is not determined : it 

 may be conjectured that they are in some way or otlier con- 

 nected with reproduction. 



The existence of motive papillaj or processes issuing from 

 the open extremities of the segments has been denied by 

 most recent observers. 



Conjugation has been noticed to occur by Ehrenberg in 

 Closterium Diance, CI. lineatum, CI. striolatum, and CI, 

 incequale. 



Ehrenberg, by whom the genus ■Closterium is placed 

 amongst the poly gastric animalcula, thus defines it: — 



" Animalia polygastrica anentera (tubo intestinali destl- 

 tuta) gymnica (non appendiculata), ct corpore uniformi in- 

 volucrato sen loricato, cryptomonadibus simillima, cum lorica 

 sponte et imperfecte dividua, hinc in polyparium bacilliforme 

 (aut fusiforme) abeuntia, j^apillis denique in lorica3 apertura 

 discretis. " 



Independently of the irregular motion of the particles 

 escaped from the cells, a circulation has been noticed, con- 

 sisting of two opposite currents, the one along the side of the 

 shell, and the other along the periphery of the internal gela- 

 tinous matter, which is invested with an elastic envelope. 



By some systematists the Closteria are placed next to the 

 ConjugatecE, with which in the occasional conjugation of the 

 fronds of two Closteria and formation of sporangia they do 

 indeed exhibit a certain degree of relationship. 



Through Closterium cylindrus Ehr., Infus. pi. v. fig. 6. 

 this genus would appear to be united to the genus Cosma- 



