746 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
bring into a collected form our information on the subject. His classifi- 
cation, however, is quite new ; five families are recognized — the Leu- 
cascidse, Sycettidas, Gran tiidse, Heteropidae, and Amphoriscidse — of these, 
as of their constituent genera, suitable diagnoses are given. 
The canal-system is found to vary considerably in what appear to be 
closely related genera ; if Dr. Dendy’s views of relationships are correct, 
the Leuconoid type has been independently evolved from the Syconoid 
type, no less than three times. The former, however, cannot be produced 
until the corticate Syconoid type has been reached ; then, the conversion 
of the originally long and radially disposed chambers into short, rounded, 
and irregular ones is such a simple matter that the change may well have 
taken place again and again. In passing from the most simple Syconoid 
type to the most complex Leuconoid there appear to have been five 
stages, which may be distinguished as the Sycetta, the Sycon, the 
Grantia, the Sylleibid, and the Leucandra-stages ; most of the genera 
are found in the Grantia-stage. No one stage is very sharply marked 
off from the one below it, and the author thinks that the five indicate a 
process of evolution which has actually taken place. 
The starting-point for the development of the skeleton is to be found 
in the radially symmetrical skeleton of Sycetta; this primitive radial 
symmetry is highly characteristic of the group, and is obviously depen- 
dent on the primitive radial symmetry of the canal-system. The first 
great change is due to the development of a dermal cortex, in which a 
special skeleton is found; the skeleton of the chamber layer of the 
sponge next begins to vary, in some cases because of the gradual change 
of the canal-system from the Syconoid to the Leuconoid type. Loss of 
radial symmetry now ensues, and the regular “ articulate ” type of Sycon 
and Grantia gives place to the irregularly scattered condition of Leu- 
candra. Other modifications consist in the development of subdermal 
sagittal triradiate or quadriradiate spicules, such as are found respectively 
in the Heteropidae and Amphoriscidae. A kind of secondary centripetal 
radial symmetry may arise owing to the development of subdermal 
radiates with inwardly directed basal or apical rays. Yery startling 
exceptions to the ordinary rules of skeleton structure are found in Sycyssa 
and Leucyssa , which appear to be due to the loss of all radiate spicules 
and the development of oxea. 
The author gives a somewhat complex phylogenetic tree of the 
Heterocoela which, it cannot be doubted, are derived from the Homocoela. 
Of the latter the more advanced types appear to be found in the radiate 
section of the genus Leucosolenia ; it is a most significant fact that, in 
the ontogeny of the simple Heterocoela, the radial tubes are formed as 
outgrowths from a central tube, exactly as in L. tripodifera. In the 
higher forms there has been a replacement of the collared cells of the 
central gastric cavity by a flattened epithelium, together with a speciali- 
zation of the skeleton, such as might give rise to the primitive Hetero- 
coele genus Sycetta. 
Histology of Sponges.* — M. E. Topsent finds that while some 
sponges, such as Desmacidon fruticosus, Heniera viscosa, and others, give 
oil’ an abundance of mucus on being taken out of the water, others, such 
* Comptes Rendus, cxvii. (1893) pp. 444-G. 
