12 Mr. W. Saville Kent on Prof. E. Haeckel’s 
bearing and flagellate extremity of the individual monads 
directed exteriorly, in the ampullaceous sacs or monad-chambers 
they are directed towards the interior of a central cavity. 
Full details, with illustrations, of the examples that have led 
to this interpretation of the “ ampullaceous sac ” accompany 
my recent communication to the Linnean Society. 
The bearing upon the whole question of Prof. Haeckel’s 
newly created group of the Physemaria may now be ap- 
proached. In Haeckel’s own words (/.c. pp. 172 and 178), 
the several types to which this title of the Physemaria is col- 
lectively applied are characterized as being neither true sponges 
nor true polypes, but as “eine kleine Gruppe von niedersten 
Pflanzenthieren, die der hypothetischen Stammform aller 
Metazoen, der Gastraea, niher stehen, als alle anderen bis 
jetzt bekannten Thiere.” Or, as elsewhere intimated, he re- 
cognizes in this group the almost perfect embodiment of the 
hypothetical “ Gastreea,”’ upon which the whole superstructure 
of his celebrated Gastreea theory is founded! Altogether Prof. 
Haeckel relegates to his newly founded group two generic and 
seven specific types, the aspect and structural characteristics 
of which, as described and illustrated by him, may now be 
examined. The first of the two genera (Haliphysema) is already 
familiar, the name having been conferred by Dr. Bowerbank, in 
his ‘ Monograph of the British Spongiade,’ ontwominute forms 
which he regarded as the smallest and simplest of known 
sponge-types; the second genus (Gastrophysema, Haeckel) 
exhibits a slight advance in complexity of structure upon the 
preceding genus. Represented in their simplest condition 
(Haliphysema primordiale et echinotdes, Haeckel), and neces- 
sarily closest approximation to Prof. Haeckel’s hypothetical 
“Gastreea,”’ these Physemaria may be described as minute sphe- 
rical orovate bodies elevated ona pedicel and bristling externally 
with adhering fragments of sponge-spicules, grains of sand, 
and other extraneously derived particles. Interiorly there is 
found a single hollow chamber opening anteriorly by a simple 
constricted terminal aperture. ‘The most interesting and im- 
portant feature of these organisms is now arrived at. By Prof. 
Haeckel’s own description and drawings it is shown that the 
entire lining surface of the simple interior cavity is represented 
by a single and continuous layer of collar-bearing cells identical 
with those that constitute the essential living units of ordinary 
sponge-structures, or of the independent Gymnozoidal Dis- 
costomatous group already described. The outer wall is 
composed of a syncytial element similar to that of typical 
sponges, with the exception that, instead of secreting a spicu- 
lar or other skeleton of its own, it draws together and appro- 
