2% THE VOYAGE OF H.M.8. CHALLENGER. 
= 
slender than in the gastrozooids, and a spheroidal tip resembling that of the tentacle of 
the gastrozooid, but smaller. The body of the dactylozooid terminates sometimes in two, 
sometimes in three tentacles, springing from a common point. 
The dactylozooids expand far more readily and quickly than the gastrozooids, of which 
latter it is comparatively difficult to obtain a view in the expanded condition. The short 
gastrozooids appear to remain perfectly quiescent when expanded, whilst the dactylozooids 
are in constant serpentine motion. The dactylozooids seldom carry their bodies extended 
straight, but usually bent in several curves; they appear to bend over towards their 
gastrozooid from time to time, as if to convey food. All the zooids are retracted on 
alarm with remarkable suddenness, disappearing entirely within the pores, 
When a portion of the coral has been placed living in reagents, it is found, after 
becoming hardened, to be bristling all over with sheaves of threads shot from the 
nematocyst around the mouths of the calicles. By some accident, on one small portion 
of a coral placed in absolute alcohol, the dactylozooids all remained partially protruded. 
This was only over a small area of about } of a square inch in dimensions, enough to 
yield a single microscopical preparation. From a very large quantity of the coral pre- 
pared in an exactly similar manner, no second preparation could be obtained, though it 
was all searched over carefully for similarly expanded zooids. This fact, however, shows 
that perhaps it might have been possible to obtain a larger quantity of expanded zooids 
in the hardened condition by the gradual addition of alcohol or fresh water to the sea- 
water in which the living animals were expanded, or by some similar means ; or perhaps 
by the sudden addition of osmic acid solution as recommended by F. E. Schulze." 
The body of the zooids, when seen in transverse section, is found to consist (PI. XIV. 
fie. 7) of an ectodermal layer, beneath which is a layer of membrane, and an internal 
mass of endodermal cells. The ectodermal layer, as studied in sections of hardened 
specimens, appears to consist of well-defined cells, most of which contain small nema- 
tocysts, whilst some contain simple nuclei. The membranous layer is apparently structure- 
less; it extends throughout the body and tentacles. Beneath the membranous layer, and 
in close union with it, are the muscular structures to be presently described, and within 
these, in the case of the gastrozooids, are, in the upper region of the body, the gastric 
cells already described. The structure of the endoderm in the lower part of the body of 
the gastrozooids, and in the dactylozooids, was not well ascertaied. In transverse 
hardened sections the body-cavity is seen to be entirely filled with the pigmented yellow 
cells, which also fill the canals of the ccenosarc. In the tentacles of the dactylozooids, 
however, of which a glance was obtained under a high power, the transverse lines or 
apparent septa, so characteristic of the Hydroids (Pl. XIV. fig. 5); and considered by 
Allman to be in reality the opposed walls of large adjacent endodermal cells, were clearly 
1 Anleitung zu wissenschaftlichen Beobachtungen auf Reisen. Herausgegeben von C, Neumayer, Hydrograph der 
kaiserlichen Adiniralitat, Berlin, 1875, Wirbellose Seethicre von K, Mobius, p, 424, 
