520 Hodgetts . — A New Species of Spirogyra. 
over the end of its corresponding cell, which at this part is slightly narrowed 
to accommodate it, the actual diameter of the vegetative filament thus 
remaining fairly uniform throughout the entire length (compare Text- fig. 3). 
The origin of this curious clamp-like organ — which, as far as the 
writer is aware, has never been described in any other species of Spirogyra 
— is as follows : The transverse septum (which is not replicate), separating 
two young daughter-cells, becomes rather thickened and biconvex in form, 
while at the same time the longitudinal cell-wall for a distance of about 
12-15 fj, on each side of the transverse wall becomes thickened to nearly 
twice its normal thickness (Text-fig. 1). Two splits now arise in the 
thickened septum, one on each side of the original ‘ middle lamella ’ 
(Text-fig. 2), which itself persists as the septum of the H-shaped connect- 
ing-clamp. Each split extends from the middle outwards, but follows the 
contour of the end of its corresponding cell, so that although originally 
transverse it turns and becomes longitudinal and finally forms the clamp- 
connexion by turning abruptly outwards just where the thickening of the 
longitudinal wall ceases, as shown in Text-fig. 3. This figure (as well as 
Text-fig. 4) shows the slight outward curl of the edges of the connecting- 
piece — a character which was fairly constant. 
The exact function of this connecting-piece is rather obscure, although 
it may be considered as a clamp-like organ tending to keep the cells of 
a filament together when excessive turgidity of the cells, or some other 
cause, is acting to produce the opposite result, i. e. the breaking up of the 
filament into its individual cells. It is clear that a cell must be pushed at 
least a distance equal to half the length of the connecting-clamp (i. e. 
a distance of about 12 to 1 5 /x) before it becomes quite free from its neigh- 
bour. Text-fig. 4 shows the ends of two disconnected cells, one of which 
has retained the connecting-piece as a sort of cap ; a state of affairs exactly 
resembling that shown in the bottom right-hand corner of Photo 4, PI. XXII. 
Photo 5 is especially interesting, since it shows a connecting-clamp — the 
septum of which is quite visible— which has just slipped off the end of 
a (curved) vegetative cell ; and moreover the latter itself is seen to have 
partly slipped out of the clamp by which it is connected to the filament. 
Since it was rather rare to find the clamp-connexions lying free in the 
water, it seems that they are generally retained by one of the cells when 
the filaments break up. 
The fibrillar structure of the external gelatinous sheath was generally 
denser round the connecting-clamps than elsewhere (see Photos 1-3, 
PI. XXII), due probably to the fact that the clamps undergo no longitudinal 
growth, while the cells themselves often attain a relatively great length. 
The cells show 5 (sometimes 4 or 6 ) narrow chloroplasts, each making 
a very lax spiral (i-ij turns), while the pyrenoids are large, projecting 
considerably from the chloroplasts, and surrounded with large angular 
