CONJUGATIONS OF DIATOMEA. 273 
Having found Navicula serians in all its stages of conjugation, I can 
now add a little more to the detail of this process in the navicular 
Diatomee, viz. the contents of the two conjugating frustules after 
having passed into the usual spherical form of the sporangium, and 
then having undergone division into the two smaller spheres, each of 
the latter becomes elongated, separates in the equatorial line, and each 
hemisphere being carried out upon the ends of the contained sporangeal 
frustule-cases in a cap-like form, remains there, until these sporangeal 
cases attain their maximum development. Pari passu, the large frustule 
is produced within all, and ultimately a longitudinal fissure, extend: 
ing throughout the frustule-case, gives exit to it by this kind of dehis- 
nee. 
Besides the three conjugations in the three different species men- 
tioned, I have found a fourth, but this is merely one of a smaller size 
of N. rhomboides; thence I may state that I have found four navi- 
cular conjugations, and, if time had permitted, I think I might have 
found more,—perhaps I may do so on a future occasion. 
But the finding of two different sizes of N. rhomboides in conjuga- 
tion, seems to throw some light on the object of this conjugating pro- 
cess in the Diatomee, and if here, why not generally on conjugating 
processes of this kind? 
Thus, the conjugating frustules of the smallest size of N. rhomboides 
produced frustules of exactly the same size as the conjugating ones 
Which produced the largest size of the same species. 
Hence it may be inferred, that the result of these conjugations by 
such repetition, is to bring the size of the frustule from its embryonal 
state up to that of its maximum development. 
After this has been attained, it appears to me that germ-cells are 
produced in the interior of the fully developed frustule, which become 
impregnated by sperm-cells, generated in the interior of the nucleus, as 
I have suggested in the freshwater Rhizopoda. The germ-cells may or 
may not come from what I have called the “ glair-nell ? in the navicular 
Diatomee, etc. 
But, should this be the case, then the result of the conjugation will 
be to bring the frustule up to the size of maturity (from which pro- 
cess arises the great diversity of size in frustules of the same species), 
and the development of the germ- and sperm-cells, with their impreg- 
nation, thus to complete the generative cycle in the Diatomee. 
VOL. II. [SEPTEMBER 1, 1864. ] T 
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