338 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
elements of Sponges does not commence quite as in other Animals. 
Some cells exhibit a tendency to change in form, extend, and fuse 
into membranes; others manifest the remarkable property of giving 
out flagelliform processes or absorbing them to form them afresh. 
All come at last to form an organism in which we find a protecting 
membrane, gastric cavities, and intermediate sustaining tissues; the 
whole is, necessarily, more or less comparable to similar formations in 
other Animals ; but this is sufficiently explained by the fact that there 
is a uniformity in the general conditions of the histogenesis and organo- 
genesis of organisms; and there is no need to invoke a tendency to 
reproduce the form of a common ancestor. M. Delage does not agree 
with those who would associate Sponges with the Coelentera ; he believes, 
indeed, that they have from the first followed a line of development 
apart from, but side by side with the line of descent of the Coelentera 
and the other Metazoa. 
There is not that opposition between the solid larvae of Siliceous or 
fibrous Sponges and the hollow larvae of the Sycandra-type that has 
been admitted by all previous writers, and that has been supposed to 
affect the destiny of the corresponding cells of the two types. In the 
former, the ciliated cells, at the time of fixation, temporarily lose their 
flagella, bury themselves in the tissues, and, after vicissitudes which 
vary in different genera, they become grouped afresh, and acquire a 
flagellum and a collar. The cells which are immediately below those 
that are ciliated, or which take part in forming the surface at the naked 
pole, are carried outwards, when they form the epidermis ; just as, in 
Sycandra, do the granular cells of the posterior pole. The species 
chiefly studied by the author were — Spongilla Jiuviatilis , Esperella 
sordida, Beniera densa , and Aplysilla sulfurea. 
Metamorphosis of Esperia.* — Dr. 0. Maas has studied the larval 
development of Esperia lorenzi O. S. When the larvae leave the mother 
by the efferent canals they ascend to the surface, and always seek the 
side of the aquarium which is towards the light. They measure about 
1 mm. in length by *55— *65 mm. in breadth, and have a yellow to orange 
pigment, which is absent at the posterior pole, and apparently, but not 
really absent at the anterior pole. The histology of the larva is de- 
scribed. In the great majority the pole which in swimming is directed 
forward becomes the base by which the larva fixes itself. In fixing there 
is a characteristic arrangement of spicules, and the larva is flattened. 
Externally there is a broad amoeboid margin of clear, flat cells forming 
a sort of network ; internally there is the still round main mass of the 
larva ; between the two lies a zone of tissue in process of transition. 
A remarkable inversion of layers follows : — the internal and inferior 
cells with small nuclei in the fixed stage are the same as the external 
elements of the free larva, and the upper external cells of the fixed stage 
are the internal and posterior cells of the free larva. There is often a 
creeping movement of the whole sponge as if it were a gigantic amoeba. 
In the next stage we have the retraction of the amoeboid margin, the 
formation of subdermal spaces, and the origin of the ciliated chambers 
from groups of small cells which formed the ciliated epithelium of the 
* MT. Zool. Stat. Neapel, x. (1892) pp. 408-40 (2 pis.). 
