H. J. Clark on the animality of Sponges. 321 
drawing the reader’s particular attention to the arguments which 
I have adduced——in the volume above mentioned—to prove the 
unity of plan in the organization of the Protozoa, and its dissimi- 
larity from any other which dominates among the four remain- 
ing grand divisions, 
most remarkable forms. I regret that words alone cannot, at 
this time, render their peculiarities as evident as I hope the illus- 
trations will, in my forthcoming paper, in the Memoirs of the 
oston Society of Natural History. 
I must ask the reader in the first place to go back with me 
almost to the Ultima Thule of animal simplicity, and revise the 
organization of the hitherto too lowly estimated Monas, in order 
to lay the foundation for the group which embraces in its limits 
80 gigantic a family as the Spongie Ciliate. o not think any 
one will be prepared to fully appreciate such a remarkable defi- 
niteness and system in the arrangement of the organization of 
onas as I have discovered among the various forms which con- 
stitute that genus. ; 
itherto a Jfonas has been looked upon as a mere shapeless 
molecule, with a vibrating cilium of some sort or other, attached 
to its surface at an indefinite point. As I understand the rela- 
tion of parts, now, the motory cilium or flagellum is perhaps the 
most remarkable feature of the whole animal, not only in a 
physiological aspect, but also in its topographical relationship. 
t me illustrate this by a description of the body and append- 
ages of Monas termo Ehr. : 
The body of that species has the form of a wide, compressed 
heart, with two distinct summits. The broad flattened sides lie 
Opposite to each other, and parallel with the plane which passes 
through the two summits, and which forms the prolongation of 
the greater transverse diameter of the body. Between these sum- 
mits is. an aperture which constitutes the mouth. One of the 
Plane which runs through the two summits, and forms, as I have 
just mentioned, the plane of the greater teaueeemue lee ial 
