148 



SCIENCE-GOSSIP. 



[July 1, 1866. 



aud in possessing, save in a few cases, terminal cells 

 containing active granules, like the genus referred 

 to. Penium, of which there are, according to 



Fig. 136. Penium digitus x 250. 



Pritchard, ten species, vary much in size and ap- 

 pearance. They are all straight, and mostly stouter 

 at the middle than at the ends ; that is to say, they 

 are cylindrical, but taper more or less towards the 



Fig. 137. End of Penium digitus (?) x 1000. 



extremities. Some species are exceedingly pretty, 

 the endochrome being arranged in fillets, or in "in- 

 terrupted divided planes radiating from the central 

 axis." From the figures we have seen, we think 



Vig. 138. — a. Penium Naviculce x 250. b. End of 

 the same x 1000. 



P. interrivptum is the most beautiful, but we have 

 not yet found a specimen, though it appears to be 

 widely distributed both in Europe and America. 



Docidium, of which about twelve species are re- 

 cognized, differs from the last in having a constric- 

 tion, more or less conspicuous, at the centre of the 

 frond, which is elongated, and terminates in abruptly 

 truncate ends, where there is always (?) a rounded 

 clear space with active granules. Among those 

 which we examined, we found one bearing a strong 

 likeness to the figure given in Pritchard and else- 

 where of D. iruncatum ; but in many examples an 

 appearance (perhaps deceptive) of cilia or setae 

 was conspicuous under the microscope. We found 

 this kind at West End, near Esher. Another (J). 



clavatum) exhibited the swarming motion so well, 

 that we endeavour to give a representation of it. 

 At certain points the moving granules were col- 

 lected in greater numbers than elsewhere. 



" 



& 





, 



Fig. 139.— a. 



* 



Docidium clavatum X 40. 

 of frond x 350. 



b. End 



The filamentous Desmidiacea are not of such 

 common occurrence in Great Britain ; having their 

 head-quarters in other countries. Still, however, 

 several species are to be met with ; and among the 

 greatest favourites is Didymoprium. This fortu- 

 nately is widely spread, but it has not as yet come 

 in our way. The numerous joints or segments are 

 somewhat barrel-shaped. There are two species. 



We found at Iveston, the pretty Uyahtheca 

 dissiliens in considerable quantity. It is enclosed 





Fig. Ii0. Hyulothtca dissiliens. 



in a thick gelatinous sheath, serving to keep the 

 joints together; for they are very fragile, and hence 

 pieces of greater or less length often occur. There 

 are two species ; one of them II. dubia, found in 

 Germany, is said to be without the mucous sheath. 

 Pritchard doubts this. 



Passing over many interesting genera of fila- 

 mentous desmids, the end view of all of which is 

 peculiar, from the arrangement of the endochrome 

 in a three-rayed, four-rayed, circular or spiral 

 manner, we come to an exceedingly pretty form, 

 Spirotania, 



It is enclosed in a somewhat egg-shaped mass of 

 mucus, and the chlorophyll is arranged in one or 

 more spiral bands. The sheath in this genus and 

 many others is difficult to be seen on account of its 

 transparency. Colouring the water is recommended 

 as a good plan for rendering it more plainly visible. 



