68 RECENT RESEARCHES IN THE DIATOMACE;R. 
and Biddulphia, “ the hoop consisted of two pieces, which at first ent 
the aceuracy of Wallich's views, and expresses an opinion that grea 
value attaches to this discovery than even to that of the bivalve character 
e 
o oop. 
In the year 1869, Dr. M*Donald, in his interesting paper “On the 
Strueture of the Diatomaceous Frustule and its Genetic Cycle" (Ann. and ; 
Mag. of Nat. Hist. 4 i 
O. ing the st 
velopment of the 
m connection with the primary valve, and the second tertiary forming 3 - 
new frustule with the secondary valve.” 
process of diminution in each successive frustule goes on until the 
minimum is reached, when the frustules conjugate, and from .this ES : 
tion arises a sporangial frustule, in all respects similar to its parents, but - 
double the size. | x d 3 
__ Within a few months after the important discovery of Dr. M'Donald 
had been made known, and before the paper had come under the notice : 
of Dr. Pfitzer, the latter had worked out the same conclusion, thae 
rati e views of Dr. M‘Donald, without derogating in n 4 
slightest degree from the credit due to himself for his own independent - 
observation. the 
It must be remarked that the theory just stated as to the nature of x | 
Mrd and its bearings on the development of the frustule, has been din: 
blished only in regard to the genus Biddulphia and its kindred fam the 3 
The supposition that the same character belongs to the heop in od, 
her humerous genera is but a presumption,—a very natural one, indeed, D 
but still it needs confirmation. die 7 
act opens up a wide field for research, and it is hoped that n 
numerous students of the Diatomacee throughout the world will 
prompted to follow out the track the discoveries of Wallich, M‘Donald, 
and Pfitzer have indicated, 
