80 Transactions of the Royal Microscopical Society. 
period in the latter. According to an American writer in ‘The 
Lens,’ whilst the process of fission in the soft parts of the diatom 
occupies only from fifteen to twenty minutes, the development 
of the valve occupies six entire days. My belief is that even this 
is an under-estimate. I need hardly point out, therefore, how 
greatly enhanced must be our difficulties in attempting to follow 
with our eye,—1, the fusion of the endochrome of the frustules 
which unite in forming the sporangial mass or masses; 2, the 
gradual development out of those masses of the sporangial frustule 
or frustules; 3, the investiture of the sporangial frustules with 
the gelatinous nidus in which they for a while rest; and lastly, 
the liberation from the sporangial frustules, whilst still retaimed 
within the nédus, of the true germs which shortly become the true 
parent frustules of the “ coming race.” 
For the present I must content myself with stating that the 
sporangial frustule is always more or less of a monster, both as 
regards dimensions* and outline; rarely, if ever, presenting the 
symmetrical outlines so characteristic of these graceful organisms ; 
that it is rarely, if ever, perfectly silicified; that the bloated ex- 
pression it exhibits is never handed down, as would inevitably be 
the case, were it the model upon which the new brood is formed ; 
and lastly, that I have never seen the slightest semblance of 
division in it, by the formation of two new valves. On the other 
hand, such incongruous characters are occasionally to be seen in the 
sporangial frustule whilst still in the embrace of the siliceous valves 
from which it sprung, as to engender a suspicion that it may be a 
Diatomacean cuckoo that has walked into its neighbouz’s nest. 
But from the contents of these giant frustules the new parents 
of the race arise :—first, in the shape of minute masses of nucleated 
endochrome ; these masses enlarging gradually in size till they 
attain the normal (but never exaggerated) proportions and outlines 
of the species to which they belong ; finally becoming endowed 
with their siliceous investiture ; and then, but not till then, earning 
the name of parent frustules. I leave it to Sir James Hannen to 
decide how far his judgments coincide with the fact that even 
before the honeymoon of the two parent valves of the diatom is 
over, they part company for ever, and if by the force of fate com- 
pelled to retain some bond of union, as witnessed in the fila- 
mentous species, they take the precaution of at all events placing 
their children and children’s children, even unto the fiftieth 
generation, as buffers between them ! 
But although the true parent frustules are never monstrous (in 
the sense of being specially created because Nature is impotent to 
restrain the gradual degeneration in size, upon which so much 
gtress has been laid, and to make amends for which so much brain 
* It sometimes is twice or even thrice the size of the largest normal frustule ! 
