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RECENT RESEARCHES IN THE DIATOMACER, 231 
for this reason, that the stipitate forms occur free and with active 
motion. As respects the substance of the stipes, it appears in this 
instance, as in the case of Cocconema and Brebissonia, in its early stage 
as a simple, colourless, well-defined gelatinous band; but in its more 
advanced stage of growth it presents a brownish central thread, sur- 
valves are formed one after the other. They are at first strongly 
arched and bent on the longitudinal axis ; the striation developes itself 
clearly in a direction proceeding from the centre towards the en 
The firstling-cells at first have girdle-bands as narrow as those in 
“Navicula, the outer larger valve, even im its earliest stage, embracing 
the smaller inner valve. After the second division, out of the bent- 
valved firstling-cells spring normal cells with two straight valves, just 
as in the ease of Navicula. The plane of separation in the firstling- 
cell is at a right angle to that of the mother-cell from which it has 
sprung—the valves of the former being seen when the girdle-band of 
ds bserver 
Rhoicosphenia. 
This may be regarded as a Gomphonema unsymmetrical in its 
three dimensions. In addition to the want of symmetry in the longi- 
tudinal and transverse axis, there occurs in this genus a, bending in 
the plane of separation, and also an unsimilarity of the two valves, of 
mpared with Gomphonema; but it 1s far otherwise 
with Achnanthes, Achnanthidium, and Cocconews: to which genera Gru- 
most strongly developed. Inthe primordial cell no remarkable distine- 
‘ddle portion of the valves is for the 
most part covered with endochrome, which is not the case in 
Gomphonema. A slight indentation is observable at the ends 
of the plate, in which there is an approach to the Coe @, 
similarly geniculated in the axis of division. The division of the 
endochrome-plate proceeds just asin‘the case of Gomphonema, towards 
which genus many transition-forms from Rhoteosphentatend. 
The formation of auxospores had been observed by Thwaites in 
