The Development, &c., of Diatomacee. By Dr. G.C. Wallich. 73 
portions of the frustular structure. It has never been my view, 
but Dr. Macdonald’s, that “7 is actually within the fully formed 
vALVE that the new half-frustule is produced” (loc. cit. p. 4). 
For then it might with perfect truth be asserted that the connect- 
ing zones are a mere surplusage, which they undoubtedly are not. 
What I maintain is that the new half-frustule is formed within the 
connecting zone of the parent valve. There is not a whit more 
reason for assuming that the new half of the frond of the just 
divided Desmid is formed within the parent half from which it is 
poured or budded forth, than there is for assuming that the new 
half of the diatom frustule is formed actually within the fully 
formed parent valve. At all events, I can unhesitatingly state that 
such an anomaly has never been witnessed by me during my some- 
what protracted acquaintance with both these families. And I would 
therefore ask for an answer to this crucial question: If the new 
half-frustule of Beddulphia pulchella or Anvphitetras antediluviana 
(two diatoms just now selected by me solely as being the giants 
of the race) is formed “actually within the parent valve”’—taking 
into consideration the fact that, just within and around the margin 
of the valves, these diatoms are deeply constricted—how does the 
infant valve (after consolidation, of course) manage to squeeze 
itself out of the narrow-mouthed cage? Should it be urged that it 
escapes before consolidation is begun or completed, it is clear that 
the fact is altogether valueless in relation to the question as to 
which part of the structure—the parent connecting zone or the 
parent valye—determines the dimensions of the new half-frustule. 
For, in that case, the moment the young pulpy infant escaped from 
its thraldom, its development could only be under the dominion of 
the connecting zone; a portion of the structure in which, as will be 
presently shown, certain other most interesting peculiarities are to 
be found in the genera referred to. 
But Dr. Macdonald expresses himself in no ambiguous language - 
on the point, for he says (Joe. ez. p. 2), “ Hach of the sliding seg- 
ments of the connecting zone is, moreover, not merely connected with 
but directly continuous with the body of its own valve, that which is 
invaginated being always the younger, having been produced within 
the other or the parent valve.” ... “Whatever may be the configu- 
ration of the true ends of the frustule, or, in other words, the body 
of the valves, the sides or ‘ hoops’ of the two forming the so-called 
‘intermediate piece, are, as it were, marginal extensions of them.” 
In reply to this statement, I venture to say that few persons 
who have studied the Diatomacez as a whole will dissent from the 
opposite view, namely, that the “‘ hoop,” be it double or be it single, 
is deciduous in the majority of the genera. Indeed, as shown in the 
extracts already adduced, there does not seem to be a single autho- 
rity, excepting Dr. Macdonald himself, who would maintain that 
