ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
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tains a gelatinous, not fluid, substance. This swells when water enters, 
and the swelling expels the thread. 
The thread often has a broader proximal portion, the axis-body, 
which may bear bristles, spines, &c. In the more primitive form of 
thread, three spiral rows of minute thickenings extend along the whole 
length, but there are many variations in this arrangement. 
The action of the nematocysts is both mechanical and chemical. 
The thread may entangle or perforate the booty, or poison it. 
The cnidoblasts which enclose the nematocysts are often somewhat 
complicated ; the peripheral layer forms a sheath, there is often a clear 
space around the nematocysts, the distal end may have a fringe of 
minute bristles, a cnidocil, &c. 
In all cases the development begins with the appearance of a small 
vacuole around the nucleus of an interstitial cell. This increases in 
size and becomes surrounded by a sheath — the outer sheath of the 
capsule. An inner sheath is then differentiated. The thread seems 
always to begin as an invagination of the capsule wall, into which a 
protoplasmic process from without penetrates. But the matter is by no 
means simple. 
Structure of Diplograptus.* — Dr. B. Ruedemann maintains that 
Diplograptus pristis and D. pristiniformis grew in composite colonies ; 
the polyparies were united in a tetraradiate stock by axial processes from 
the ends hitherto regarded as distal. The siculae were always at the 
outer ends. The bases of the polyparies, of which as many as forty 
might be united, were surrounded by the “ funiculus,” which was 
enclosed in a capsule, the “ central disc” of Hall. 
Round the central disc was a whorl of (4-8) chitinoid vesicles, which 
enclose the siculae. The latter have their broad ends outwards, and 
each is connected by a thread-like process with an axial club-shaped 
body inside the vesicle. It is supposed that the vesicles are gonangia, 
and the club-shaped bodies blastostyles. 
Over the whorl of gonangia lay a hemispherical vesicle with a 
quadrangular basal plate, probably a swimming organ. 
The siculae seem to have been liberated when ripe, and were at first 
without hydrothecae. Those with two hydrothecae show a four-cornered 
chitinoid plate — the future pneumatocyst — at the thread-like process of 
the sharp end. At the attachment of the pneumatocyst there is a small 
knot, from which funiculus and central disc arise. Before half-size is 
attained, gonangia are recognisable around the central disc. 
The siculae which arose from these gonangia remained in partial union 
with the central organs and grew into new branches. The polyparies 
grew backwards, and the ne v hydrothecae were always formed at the 
basal end of the polypary. 
The whole colony was borne by the chitinous air- vesicle with a 
quadj angular basal plate ; below this lay a chitinous capsule, the central 
disc, enclosing the funiculus; the central disc was surrounded by a 
whorl of gonangia which enclosed siculae ; below this whorl, and pro- 
ceeding from the enclosed funiculus, hung the convex-concave tuft of 
polyparies. It does not appear, however, that the actual observational 
basis for these very precise generalisations is as yet very broad. 
* Ber. Gesellsch. Freiburg, ix. (1895) pp. 174-5. 
