The Development, &c., of Diatomacee. By Dr.G. C. Wallich. 65 
In the latest (1875) edition of Dr. Carpenter’s treatise ‘ On the 
Microscope’ (p. 307), the description of “the hoop” is, in every re- 
spect, essentially the same as that just quoted from the ‘ Micrographiec 
Dictionary.’ But the author adds that, as soon as the newly formed 
frustules begin to undergo any increase, “ the valves separate from 
one another, and the cell-membrane, which is thus left exposed, 
immediately becomes consolidated by silex, and thus forms a sort 
of hoop.” Indeed, so evidently is this portion of the structure 
still regarded by Dr. Carpenter as single, that, whilst in the letter- 
press describing the woodcut of Biddulphia pulchella (at p. 313), 
no allusion of any kind is made to the double nature of the 
connecting zone, the characteristic nature of the appearances pre- 
sented by the overlapping margins have been very fairly depicted 
by the artist. The same singular oversight is repeated with regard 
to the distinct appearance presented by the overlapping zones in 
the woodcut of Grammatophora serpentina (at p. 323), a diatom 
in which, considering its comparatively small size, the true com- 
position of this portion of the structure is very readily discernible. 
“In Melosira,” Dr. Carpenter continues, “and perhaps in the 
filamentous species generally, the hoop appears to keep the frus- 
tules united for some time. This is, at first, the case in Bid- 
dulphia and Isthmia, in which the continued connection of the 
two frustules by its means gives rise to the appearance of two com- 
plete frustules having been developed within the original; subse- 
quently, however, the two new frustules slip out of the hoop, which 
then becomes completely detached, and the same thing happens 
with many other diatoms, so that ‘the hoops’ are to be found in 
large numbers in the settlings of water in which these plants have 
long been growing.” 
And finally, Dr. Carpenter mentions that Professor W. H. 
Smith (U.S.), in the second part of his “ Memoir on the Dia- 
tomacez,” published in ‘The Lens’ (in 1872), regards the 
Diatomaceze as siliceous boxes, with one portion (the cover) 
slipping over another, as in Pinnulariw, or with edges simply 
opposed, as in Fragillariz. In the formation of the new valve 
the new part, which slips out from the older, is somewhat 
smaller, . . . . the part which slips out carrying away one of the 
old valves ; and by further self-division, the new valve becomes 
smaller and smaller, as stated by Braun. At this period conjuga- 
tion takes place, and a return to the normal condition of the 
original large frustule by the formation of a Sporangial frustule 
double the size of the parent frustules (op. cit. pp. 314, 315). 
Thus far it has been my particular aim to quote, as nearly as 
possible in the original words, the opinions expressed in two of the 
most recently published standard works on microscopic subjects, 
regarding conspicuous and important portions of the frustular 
