122 
TOPULAR SCIENCE REVIEW. 
place is unquestionably adjacent to the more simple unicellular 
Protozoa, including the ordinary monads, Rhizopoda, and Infu- 
soria. The fuller light so much needed to determine once and 
for all this abstruse but exceedingly interesting question of the 
true nature and affinity of the sponges, has without doubt been 
considerably obscured through the absence, since the death of 
Prof. Clark, of all further testimony or corroborative evidence 
relative to those independent collar-bearing monad forms upon 
which his arguments were essentially based, and which, if his 
views were correct, nrght be expected on a closer and more 
extended acquaintanceship to yield parallel structural and deve- 
lopmental data of the greatest importance. This hiatus in the 
chain of evidence was early recognized by the writer, and may 
be said to have directly led to the investigations pursued in 
reference to this group within the past five or six years, result- 
ing in the discovery of the innumerable previously unknown 
species, many of which are figured for the first time in these 
pages. Having this amount of material available for correlation 
and comparison, the case for the advocates of the protozoic 
nature of all sponges has been immeasurably strengthened, 
while little if any substantial foothold would seem to be now 
left for the adherents of the opposite or coelenterate persuasion. 
Examining numbers of sponges and comparing the structure 
and manifestations of their collar-bearing unicellular constituents 
with those of the solitary or colony-forming individuals of the 
genera Codosiga , Saljpingceca , and others previously referred to, 
the phenomena elicited were found to be altogether identical. 
Every separate collar-bearing cell in these sponge-structures 
was found in a similar manner to possess a separate and inde- 
pendent existence, capturing its food in the same manner 
with its exquisitely hyaline wineglass-shaped trap of circulating 
sarcode, possessing the same posteriorly situated and rhythmi- 
cally opening and closing contractile vesicles, dividing by lon- 
gitudinal or transverse fission, and ultimately encysting and 
breaking up into countless germs or spores destined to grow to 
individuals identical with the parent form, and further extend the 
borders of the commonwealth. In common with the independent 
collar-bearing types, these sponge-monads were found also to be 
possessed of an equal or even greater amount of plasticity of 
external form, retracting their characteristic collar and flagellum, 
and assuming an amoeboid aspect in a manner closely identical 
with what has been already described of Salpingoeca amphori- 
dium and fusiformis . Often, again, these sponge monads (see 
Plate III. fig. 31), having the collar and flagellum withdrawn, 
throw out long, slender, capitate processes, which communicate to 
them an appearance closely resembling that of certain of the 
suctorial animalcules or Acinetce. 
