115 



The Closterium acuminatum presents an other 

 instance of this exchange. In all the Closteria, seen 

 sidewise, and where the two half cuirasses join, we 

 discover two holes (fig. 57. 67. d. d. fig. 59. d. d. 

 fig. 61. c.) opposite one another. The destination 

 of these two openings was long for me a matter of 

 doubt, till I could at last distinguish the junction 

 of the Closterium acuminatum, in which two animal- 

 cules (fig. 59.) placed themselves obliquely one 

 against the other, and till I saw, through these 

 openings, the exchange of a transparent and scarcely 

 perceptible fluid. In this union, we see also upon 

 the cuirass an opening, both on the clear and on the 

 convex side. This opening, however, is only visible 

 during the union, described (fig. 59. x.). At all other 

 times , in spite of all sorts of trials , I never could 

 distinguish any thing. 



The genus Echinella Ehrenb. (fig. 54 55.), be- 

 side the orifice (fig. 55. a.) , has upon each cutting 

 surface of its body, three lateral pores, consequently 

 sex in all (fig. 54. 55. b. b. b.), passing through the 

 cuirass. Though closely adhering together by these 

 small cutting surfaces , I never could discover any 

 exchange of fluids operated by these pores. 



The propagation of the Oscillatoriae and Diato- 

 meae is probably performed by decomposition of the 

 parts 5 I never saw, however, propagation take place 

 by division, admitted and even described by several 

 naturalists, such as it may be seen in Infusoria of 

 a higher category, and such as it has been admirably 



