I N T RO D U C T I O N .
S e c t i o n VIII.
R e pr o d u c t io n in t h e D ia t o m a c eæ .
I HAVE already said (Introduction, vol. i. p. xxviii) that “ the
circumstances which accompany the reproduction of the Diatomaceæ
are too imperfectly understood to permit me to
employ them, as I ought otherwise to have done, in the generic
arrangement of the species.” The three years which have
elapsed since I penned this sentence have not materially added
to the knowledge then possessed on this interesting portion of
our inquiry. The phænomena which attend the formation of
the reproductive body are still altogether unknown in many
genera, and are only partially understood even where they have
been best observed and most carefully recorded.
The little hitherto known upon the subject is primarily due
to the researches of Mr. Thwaites, abruptly terminated by his
removal to another and wider field of labour, amidst the more
luxuriant and attractive vegetation of a tropical climate.
In July 1847, Mr. Thwaites announced, in the pages of the
‘ Annals of Natural History,’ that he had discovered, in the
May of that year, a species of the Diatomaceæ, viz. Eunotia
tiirgida, Ehr. [Epithemia turgida, Kiitz., and Synop. B. D. vol. i.
fig. 2), in a state of “ conjugation.”
He was led to adopt this term from the analogy which the
process he had detected bore to that occurring in the Des