Algae, whicli he had preserved for examination in a separated
and confined condition.
Tlie above comprises all the information on the present subject
hitherto accessible to the English reader, if we except a few
remarks on the physiology of the process in Professor Braun’s
‘ Rejuvenescence in Nature ’ (published by the Ray Society
1853X and which refer rather to tlie facts recorded by Mr’
Thwaites, than to personal observations of the ingenious writer.
I now proceed to record the various examples of the conjugating
process which have fallen under my own observation, and
to deduce from tlie whole such conclusions respecting its nature
and significance as may appear legitimate and necessary. I
shall mention, in the order of their systematic arrangement, the
species in wliich I have noticed conjugation, with the date of
the observation, and shall add a reference to the figures in the
Plates of the present volume which illustrate the process under
its various modifications :—
1. E p i t h e m ia TURGIDA, W. Sm.. September 1847. Plate A f ie 2 I-TV
(from Thwaites). ' ’
2 . E p i t h e m ia Z e b r a , October 1848.
3. „ SoREX, Kiitz., May 1851. Plate A. fig. 9. I. U.
4. „ GiBBA, Kiitz., September 1847. Plate A. fig . 13. I. U
5- » y e n t r ic o s a , Kiitz., November 1853. Plate A. fig. 14.1,'H
6. C o c c o n e is P l a c e n t u l a , Ehr., February 1853. Plate B. fig. 32. l .- i v '
7. C y c l o t e l l a K u t z in g ia n a , Thw., November 1848. Plate B. fig 47'
8 . C o c c o n e m a l a n c e o l a t u m , Ehr., January 1850 and Anril 1 8 5 9
Plate C. fig. 219. ^
9. C o c c o n e m a C is t u l a , Ehr., August 1850 and April 1852 Plate C
fig. 221.1. II.
10. C o c c o n e m a p a r y u m , W. Sm., April 1850.
11. G o m p h o n e m a d ic h o t o m u m , Kiitz., August 1850. Plate C. fig . 240.
12. „ TENELLUM, W. Sm., March 1853.
13. „ OHVACEUM, Ehr., March 1850, April 1852 and March
1853. Plate D. fig. 244. I.-IV.
1 4 . G o m p h o n e m a c u r v a t u m , Kiitz., March 1 8 4 9 . Plate C. fig. 2 4 5 . I.-IV.
15. „ MARiNUM,W.Sm., March 1852. Plate D. fig. 246.1.-V."
16. H im a n t id iu m p e c t in a l e , Kiitz.,October 1847. PlateD. fig.2S0.I.-IV
(from Thwaites).
17. A c h n a n t h e s l o n g i p e s , Ag., July 1849.
18. ^ „ A W. Sm., March 1852. Plate D. fig. 300 A
19. R h a b d o n e m a a r c u a t u m , Kiitz., November 1849 and March 1852.
Plate E. fig. 305. 1.-III.
20. M e l o s ir a n u m m u l o id e s , Kiitz., October 1852. Plate XLIX. fig.
3 2 9 ./'.
21. „ B o r r e r i i , Grev., March 1852. Plate L. fig. 330.
22. „ s u b f l e x i l i s , Kiitz., March 1852. Plate LI. fig. 331.
23. „ VARiANS, Ag., October 1851. Plate LI. fig. 332./. «p.
24. O r t h o s i b a o r ic h a l c e a , W . Sm., October 1855. Plate E. fig. 337.
I.-IV. (from Thwaites).
25. E n c y o n e m a PROSTRATUM, Ralfs, April 1852. Plate E. fig. 345.1. & II.
26. CoLLETONEMA SUBCOH.ERENS, Thw., October 1847. Plate E. fig. 353.
27. ScHizoNEMA G r e v i l l i i , Ag., July 1849. Plate E , fig. 364.
If we add to the above iist Navícula jirma, Kiitz., and Surirella
bifrons, Kiitz., as recorded by Dr. Griffith, together with
Cocconeis Pediculus, Kiitz., Cymbella Pedicuhs, Kiitz., and Am-
phora ovalis, Kiitz., detected by Mr. Carter, we shall have in all
thirty-two species belonging to seventeen genera, which have
been observed in a state of conjugation. These numbers are
small in proportion to the whole of our ascertained British
forms, and leave much to be accomplished by future observers.
One reason for the paucity of observations on this process in
the Diatomaceæ is no doubt to be found in the changes which
usually take place in the condition of these organisms at this
period of their existence. Dining conjugation the progress of
self-division is arrested, the general mucus-envelope or stratum,
produced during self-division, is dissolved, and the conjugating
pairs of frustules become detached from the original mass ;
they are thus more readily borne away and dispersed by the
surrounding currents, or the movements of worms and insects,
and their detection becomes in consequence more casual and
difficult. By far the greater number of the species I have mentioned
belong to those genera whose frustules are adherent or
attached by stipes to foreign bodies, or which form continuous
filaments or aggregated frondose expansions. Not more than
four, viz. Cyclotella Kutzingiana, Naviculafirma, Amphora ovalis,
and Cymbella Pediculus, are to be regarded as free forms : the
reason I have just given will account for this circumstance, and
the larger proportion of adherent or frondose species detected in
conjugation may doubtless be ascribed to the firmer position