MORPHOLOGY. 
Goel. 9 
bearing the male sexual products. The same author gives a preliminary 
, note (43) on the male gonangia of Allopora and Distichopora. (A more 
complete description, with illustrations of these structures, has been pub- 
lished in the Q. J. Micr. Sci. 1891.) 
Viguier (88) gives an elaborate account of the remarkable Hydro- 
medusan Tetraplatia volitcins, and asserts that it is impossible to give it its 
proper position in classification until the whole of its life-history is known. 
Bigelow (8) fiuds that in Pelagia, Chrysaora , and Dactylometra , with 
increased complexity in the general characters, there is, both phylogenetic- 
ally and ontogenetically, an increase in the complexity of the marginal 
organs, but the steps in the ontogeny are not strictly identical with the 
conditions at the corresponding points in the phylogeny of the species. 
The same author (7), in describing some physiological experiments on 
Caravella , states that there was no rhythm observed in the contractions 
of the tentacles, but the cormidia contracted at the rate of eight con- 
tractions a minute. Exposure to unfavourable conditions causes the 
appendages to become detached, even while still alive. The cormidia 
may be cut into small pieces, and each piece retain its vitality. The 
food consists of small fish. 
Claus (16, 17) fiuds that the embryonal development of Cotylorhiza, up 
to the gastrula stage, takes place within the egg-membrane. There is no 
irregular immigration of cells into the blastula cavity, which is formed by 
invagination. The young Scyphostoma forms the proboscis very early, 
and before the formation of the four perradial tentacles. In distinction 
to Hydroid polyps, the young Scyphostoma is characterised not only by 
the ectodermal nature of the proboscis, but also by the production of four 
diverticula of the stomach and an even number of tamiolae. The four 
septal muscles originate by the immigration of ectoderm cell-knobs 
from the peristom, and come secondarily into relation with the tseniolse. 
The multiplication by stabilisation is a form of “ alternation of genera- 
tions.” 
Wagner (89) gives some further details of the structure of the interest- 
ing Hydrozoon, Monobrachium parasiticum. In the centre, the colony 
is almost entirely composed of sexual individuals ; between the centre 
and the periphery these are mixed with hydranths, and at the periphery 
itself there are some special forms called pseudo-nematophores. The 
pseudo-nematophores represent probably the spiral zooids of Podocoryne 
and Hydractinia. The ectoderm shows signs of degeneration due to 
parasitism; in the absence of a sub-epithelium there is an absence of 
nervous system and an almost complete want of differentiation of the 
cells. The endoderm of the tentacles shows a condition intermediate 
between that of solid and hollow tentacles. 
The Keimstatte is the hydrorhiza. The sexual cells pass along the 
endoderm to the ventral ectoderm of the radial canals. This is, then, 
one of the rare cases of the migration of the sexual cells in a form with 
a fully developed medusa. 
Lo Bianco & Paul Mayer (64) announce that they have been able to 
