THE 
MONTHLY MICROSCOPICAL JOURNAL. 
FEBRUARY 1, 1877. 
I.—On the Relation between the Development, Reproduction, 
and Markings of the Diatomacee. By G. C. Watutcx, M.D., 
Surgeon-Major, Retired List, H.M. Indian Army. 
(Read before the Royau Microscopical Society, January 3, 1877.) 
Puates CLXXI. anp CLXXII. 
Ar the close of a paper ‘‘ On the Structure and Development of the 
Diatom Valve,” laid before the Royal Microscopical Society in 
December 1859, I drew the following conclusions from certain 
facts referred to in that and a prior paper “On Triceratiwm,” in 
which the same points had been incidentally discussed by me: 
“That the growth of the diatom valve ceases entirely, either at 
the period of its liberation from the connecting zone of the parent 
valve, or immediately afterwards.” 
EXPLANATION OF PLATES CLXXI. AND CLXXII. 
Puate CLXXI. 
(N.B.—The figures in these Plates are, to a certain extent, diagrammatic; 
all such markings and details as are calculated to obscure the parts specially 
under notice having been omitted.—G. C. W.) 
Fic. 1.—Two frustules of Biddulphia pulchella, in which division has just been 
completed : p.v.a and p.v.b, the primary valves of the parent frustule ; s.v., s.v., the 
two secondary or newly formed valves; P.c.z.a and P.c.z.b, the connecting 
zones of the parent valves; d, the double or overlapping portion of the connecting 
zones; x, 7, the marginal row of puncta of the connecting zones. 
Fic. 2.—A frustule of same, with the connecting zone of the primary valve of 
the parent frustule still adherent. 
Fre. 3.—A primary or parent valve, within the connecting zone of which the 
new valve is being developed by gemmation. 
Fic. 4.—A similar valve and its connecting zone separated from each other: 
g, the deep groove or channel encircling the free margin of the valve, into which 
the inverted edge of the connecting zone dips. 
Fic. 5.—A valve of same, showing the buttress-like thickenings which give 
the valve of this and some allied species of Biddulphia the appearance of being 
divided into Jocu/i. 
Fic. 6.—A frustule of Zsthmia nervosa, in which division is about three parts 
completed: p.v.a and s.v., primary or parent, and secondary valves. 
Fic. 7.—A frustule of the same in which division is completed. The con- 
necting zone of the parent valve still adherent, within which the secondary or 
new valve s. v.b was formed. Crossing the centre of the frustule may be seen the 
two new connecting zones already considerably developed. On their attaining 
mature dimensions the parent connecting zone generally becomes detached. 
Frc. 8.—A frustule of Biddulphia turgida, showing the shallow saucer-like valve 
in this species, with its two horns and two T-shaped spines. 
Fic. 9.—A detached valve of same, showing a minute but very definite 
VOL. XVII. F 
