July 1, 1SGG.] 



SCIENCE-GOSSIP. 



149 



Doubtless different positions of the mirror, and 

 modifications of the light by means of the stage- 

 diaphragms, tend to the same end. Pritchard 



Fig. 141. Spirotania condensata x 300. 



acknowledges four species of SpiroUenia. Two of 

 them appear to be restricted to the Continent of 

 Europe. 



While examining our collection from Keston on 

 several occasions, we met with solitary examples of 



3 



a b 



Fig. 142. Staiirasti/m dejectum x 230.— a. End 

 view.— b. Side view. 



the numerous genus Stan rash -urn. Their habit is 

 said to be to attach themselves to the stems and 

 leaves of aquatic plants; there abiding indelicate 



Fig. 143. Staurastrum gracile (?) x 250.— a. End 

 view.— b. Side view. 



clouds which the slightest touch is sufficient to 

 disperse through the water. Eor this reason it was 



hardly expected that we should find any Stauras- 

 trum in this locality, unless in the ponds. The 

 species, seventy-three or thereabouts in number, in 



a b 



Fig. 144. Staurastum spongiosum x 250.— a. Side 

 view. — b. End view. 



some cases approach Comarium, but many examples 

 are very different. Often they are furnished 

 with projecting spines which make their shapes 



Fig. 145. 



a b 



Staurastum alternans x 250. — a. Side 

 view. — b. End view. 



still more fantastic. The figures representing both 

 the end and front views of the species we saw, will 

 give a better notion of them than a verbal des- 

 cription. 



They are all minute, and thus liable to be over- 

 looked if a quarter-inch objective be not employed 

 in the search. We found one curious example of 

 self-division. 



The result of conjugation in Demidiacece, viz., a 

 Sporangium, is generally spherical. Its surface is 

 very often studded with eminences or forked spines. 

 Mr. Ealfs, speaking of the development of these 

 curious bodies, says, "the Sporangia I consider cap- 

 sules, and this view seems to be confirmed by the 

 experience of Mr. Jenner, who states that the cover- 

 ing of the Sporangium swells, and a mucus is 

 secreted in which minute fronds appear, and by 

 their increase at length rupture the attenuated 

 covering ; " then Brawn, also quoted by Pritchard, 

 writes respecting the same obscure subject, 

 " certain early conditions observed in Closterium and 

 Et/astrum, namely, families of unusually small hidi- 



ng. 146. Euastrum didelta. 



viduals enclosed in transparent colourless vesicles, 

 render it even probable that in certain genera of 

 Demidiea, a number of individuals are produced 

 from one spore by a formation of transitory genera- 

 tions occurring already within the spore. The 



