216 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
method or is it a secondary modification of a still earlier phenomenon. 
The author believes that the Ilexactiniae are descended from forms whose 
ova possessed a relatively large amount of food-yolk. The original con- 
dition is found in the Alcyonaria, and the more typical delamination of 
the Hexactiniae has been derived from this. In Renilla the central cells, 
heavily laden with food-yolk, are separated from the proportionately 
more protoplasmic ectoderm ; later, a certain number of the cells become 
transformed into the endoderm layer, while the rest degenerate, and 
their contents serve as food for the developing embryo. This, though 
to a less extent, is seen in Manicina. In Metridium the yolk is much 
more reduced, so that the blastula cavity never becomes filled up ; the 
delaminated cells are almost all converted into the definite endoderm, 
a few only disintegrating and giving rise to the granules of food-yolk 
which lie in the endodcrmal cavity. 
The next subject discussed is the formation of the first eight mesen- 
teries in Rhodadis. So far as can be judged it would appear that in Rho- 
dadis there is no reflection of the stomodeeal ectoderm in connection with 
the formation of the mesenterial filaments, and in Auladinia the evidence 
points in the same direction. The essay concludes with an account of 
some later stages in Auladinia. They lead to the conclusion that the 
median streak was the first to make its appearance in the ancestors 
of the Actinozoa, who remained for some time with simple glandular 
filaments, formed by a differentiation of the endodermal cells along the 
free edges of the mesentery. Later on, the ciliated respiratory portions 
of the mesentery developed by a down-growth of the stomodeeal 
ectoderm ; they were first confined to the upper portion of the mesen- 
tery, where the glandular streak was not developed, but, later, they 
extended their limits, came to overlap the glandular portion, and gave a 
trilobed form to a portion of the filament. 
Revision of British Actiniae.* — In the second part of his revision, in 
which Prof. A. C. Haddon has had the assistance of Miss A. M. Shackle- 
ton, the Zoantlieae are dealt with. This is a group in which it is above 
all things necessary to combine anatomical and microscopical examina- 
tion with the methods of the older zoologists, for the species of Zoantlieas 
can only be established after sections have been cut and studied. The 
authors point out that the identification of new material with recognized 
species requires the utmost circumspection. A useful account is given of 
the general anatomy of the group ; of the mesogloea it is noted that its 
ground substance is always homogeneous ; it is perforated by numerous 
minute cells which are sometimes star-shaped, but more often produced at 
each end into a long fibril which extends in a radial direction. Some of 
the fibrils are undoubtedly connected with the ectoderm, and others with 
the endoderm. The base of the endoderm forms a feeble but complete 
muscular sheath ; this becomes converted in the capitular region into a 
sphincter muscle, which in contraction causes the introversion of the 
corona and capitulum. 
It is proposed to divide the Zoanthidae into two, new, subfamilies to 
be called Brachyneminae and Macroneminae ; the former have the sulcar 
element of the primitive sulco-lateral pairs of mesenteries (cnemcs) 
* Scient. Trans. R. Dublin Soc., iv. (1891) pp. 609-72 (2 pis ). 
