392 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
fathoms in the Sagami Sea, distinguishable by the presence of very long 
spines on the abactinal, and of hoof-capped spines on the actinal side ; 
and A. Ijimai , distinguished by the peculiar arrangement of the primary 
tubercles. 
Ccelentera. 
Structure of Hydractinia.* — Miss M. C. Collcutt has studied the 
structure and relative positions of the coenosarc and chitinous parts in 
Hydractinia echinata. The chitinous skeleton is for the most part a 
continuous irregular crust attached to some foreign body, and overlaid 
by a coenosarc consisting of two layers of ectoderm, enclosing between 
them a number of branching and anastomosing endodermic tubes. These 
tubes are connected at intervals with the endodermic canals of the 
polyps, the upper layer of ectoderm being continuous with the ectoderm 
of the polyps. 
As is well known, the colonies are common on whelk-shells inhabited 
by hermit-crabs. A large colony may cover the whole shell except the 
roundish patch which rubs along the ground ; a small colony is usually 
situated near the edge of the shell ; a Polychaete worm, Nereis bilineata , 
was always found along with the hermit crab. 
A colony consists of— (1) gasterozooids or nutritive polyps, (2) blasto- 
styles or reproductive polyps, (3) dactylozooids or spiral polyps, and 
(4) tentacular polyps. The gasterozooids are naturally most numerous, 
but in early spring and in summer the blastostyles increase greatly in 
numbers, and at these times give rise to the genital products. The 
colonies are either male or female. The dactylozooids are situated 
around the shell mouth ; they are capable of coiling themselves spirally, 
and may function as defensive polyps. Miss Collcutt has succeeded 
in demonstrating the presence of a mouth, which Allman and Strethill- 
Wright failed to notice. She also gives evidence of the migration of 
ova between ectoderm and endoderm in the blastostyle. The histology 
of the two layers is described in detail. 
Stinging Cells, f — Prof. R. von Lendenfeld furnishes an up-to-date 
account of the stinging-cells of Cnidaria. He gives a list of the litera- 
ture since 1887, and then sums up the facts in regard to the structure, 
development, and function of the elements in question. 
Among the steps of progress the following may be noted. The 
stinging cells are either modified gland-cells (Lendenfeld and Schneider), 
or modified epithelial cells (Iwanzoff). There is an essential difference 
between nematocysts and spirocysts (Bedot). The muscular nature of 
the stalk (Chun) has not been confirmed ; it is doubtful whether even 
the mantle is muscular. All later authors agree that the wall of the 
capsule is two-layered. According to the majority, the thread is a con- 
tinuation of the inner layer ; Iwanzoff represents the opinion that it is a 
continuation of the outer, or of both. The spirocyst thread is always 
smooth; the nematocyst-thread has normally three spiral ridges of 
spines, usually larger at the base. They probably increase the thread’s 
power of penetrating and boring. As to the explosion, the hygroscopic 
nature of the capsule contents explains the increased tension when water 
* Quart. Journ. Micr. Sci., xl. (1897) pp. 77-99 (1 pi. and 3 figs.), 
t Biol. Centralbl., xvii. (1897) pp. 465-85, 513-30. 
