ANATOMY, EMBRYOLOGY, THYSIOLOGY, BIOLOGY. Spong. 18 
point.] To the four categories of spongin fibres distinguished by Kol- 
liker, should be added a new form of fibre, with fibrillar structure 
(A carmts). In Pscimmoplysilla arabica the cortical sheath is wanting, 
and the whole fibre consists of medulla, showing distinct stratification. 
In Spirastrella decumbens there is a basal plate formed of a thin lamella 
of spongin. In Stelletta siemensi there are spongin spheres. The organi- 
zation of Sponges is as favourable a compromise as possible between the 
principles of nutrition and firmness. In Euplectella the power of bear- 
ing loads (i.e., particles falling from above) is increased by the longi- 
tudinal tracts of spicules, held together by circular ribs. In addition, 
there are two systems of ribs, running spirally and crossing at a right 
angle. Their direction corresponds exactly to the curves of pressure and 
pull upon a hollow cylinder, which is fixed at one end and free at the 
other, when acted upon laterally by a force directed perpendicularly to 
the long axis of the cylinder. In Euplectella suberea the curves of pres- 
sure and pull are exceedingly regular, and the Sponge is fitted to resist 
pressure in all horizontal directions. In Euplectella aspergillum the 
curves often run irregularly in the upper part of the Sponge, but in some 
specimens are quite regular. In the former case the cornucopia-shaped 
Sponge has only feebly projecting spiral curves on the convex side, but 
strong ones on the lateral parts. This shows that the pressure caused 
by horizontal water currents works from one side, and is directed against 
the convex side. For the author’s views on the effect of vertical distribu- 
tion upon spongin structures, see Keller (1). 
von Lendenfeld (1) details many facts in the anatomy and histology 
of the Calcareous Sponges. Ascetta clathrus is described under four 
forms, a (pp. 211 & 212), b (pp. 212 & 213), c (pp. 213 & 214), and d (pp. 
214 & 215), which appear to succeed one another in postembryonal 
development, and are therefore not to be regarded (with Haeckel) as 
distinct varieties. In the forms B, c, and d the endoderm is many 
layered. The author believes that from the larva is produced Form A, 
which produces by budding Form B, in which the sexual cells ripen. 
During this process the Sponge loses its pores and passes into Form c, 
and finally into Form n. The latter form represents a resting condition 
of the Sponge, and during its growth the embryos ripen and leave the 
Sponge. All forms are without oscula, as were also all the specimens 
observed of Ascetta cerebrum (p. 208), A. blanca (p. 218), and Ascandra 
reticulum (p. 223), and many specimens of other Ascons. In Homandra 
falcata (= Ascandra falcata, H.) a peculiar kind of canal system is 
described (pp. 230 & 231). Small pores on the surface lead into narrow 
canals. These unite into larger, irregular, short stems, which open into 
a subgastral system of lacunes. Numerous pores put these lacunes into 
connection with the gastral cavity. In younger examples pores on the 
surface lead directly into the gastral cavity. In Sycantha tenella (p. 236), 
the flagellated chambers, which are long and narrow, do not all com- 
municate directly with the gastral cavity, but are united in groups, and 
the water goes from one chamber to another before reaching the gastral 
