728. 
and especially those of the Hydroids. He dis- 
covered the peculiar structure of the lasso- 
cells of the Ctenophore.” 
During this time Clark began the serious 
study of the Protozoa, undoubtedly compelled 
to do so in order to properly interpret the his- 
tological facts then accumulating in the 
study of the Radiates. After leaving Cam- 
bridge he studied the Infusoria and lower 
plants, and made drawings and notes com- 
prising descriptions of many new forms of 
Infusoria. He planned an extensive work 
upon this subject, which, had he lived to com- 
plete it, might have equalled if not surpassed 
Claparéde and Lachmann’s famous work on 
the Infusoria. He did not dissociate the Pro- 
tophyta from the Protozoa, regarding them as 
almost inseparable in nature; thus, in his lec- 
tures to his classes, well nigh anticipating 
Haeckel’s classification of the lowest forms of 
the animal and vegetable kingdom into the 
Protista and Protozoa. 
In his first paper on Actinophrys (1863) he 
announced the discovery that “all vibratile 
cilia originate in the amorphous. intercellular 
substance,” and do not form direct prolonga- 
tions of cells, 7. e., that cilia are prolonga- 
tions or extensions of the protoplasmic sub- 
stance of the cells from which they arise. 
The same year he discovered the eggs of 
Tubularia, and showed that there was but one 
type of development in the Hydromeduse 
(excepting the Narcomeduse and’ Trachy- 
meduse), and that the differences observed 
in the developmental process were merely 
modifications of degree and not of kind, an 
exceedingly valuable addition to our knowl- 
edge of the affinities of the various groups of 
Hydromeduse. 
Foremost, perhaps, among his several dis- 
coveries with the microscope was that of the 
true nature of the cilio-flagellate infusorians 
and the sponges. In 1866 appeared a brief 
paper, entitled “Conclusive Proofs of the 
Animality of the Ciliate Sponges, and of their 
Affinities with the Infusoria Flagellata.” 
While Clark had endeavored to show in his 
Lowell Lectures that there was a unity of 
plan in the organization of the Protozoa, their 
SCIENCE 
[N.S. Vou. KXXV. No. 906 
bodies being arranged in the form of a helix, 
he now endeavored to prove that the sponge 
did not depart from the protozoan type. In 
the full memoir, published about a year later, 
under the title “Spongie Ciliate as In- 
fusoria Flagellata,” he attempted to establish 
the homology of the flagellate cells of the 
sponge with the flagellate Infusoria. His dis- 
covery of the flagellated cells of living sponges 
and demonstration of their animal nature was 
a great step in advance of previous observers. 
While, as Clark observes, Carter had first de- 
tected the true criterion of their: animality, 
this was confirmed and demonstrated still 
more completely by Clark himself, as acknowl- 
edged by Carter in his “Confirmation of 
Professor James-Clark’s ‘Discovery of the 
True Form of the Sponge-cell (Animal).” 
The Choanoflagellata, or collar-bearing fla- 
gellate animalcules, were discovered by Clark, 
and his further discovery that the flagellated 
(ciliated) chambers of sponges are lined by col- 
lared cells of the same peculiar structure as 
the individual Choanoflagellata, led him to 
regard the sponges as colonies of Choano- 
flagellata. The views maintained by Clark 
with reference to the position and affinities of 
the sponges were, that these organisms must 
be regarded as compound colonial forms of 
Flagellata, whose units, in the case of Deu- 
cosolenia, exhibited a type of structure essen- 
tially similar to that of Codosiga and Sal- 
pingeca—genera established by him to receive 
his collared cell forms—but might possibly in 
other instances more closely approximate to 
that of Monas (Spumella) Bicoswca or An- 
thophysa. In these views he was supported 
by the observations of Saville Kent and Stein, 
and in the main by those of Carter and to a 
less extent by Balfour, but opposed by 
Haeckel and F. E. Schulze. The subsequent 
discovery by Saville Kent of Proterospongia 
(Savillia) at that time rendered the deriva- 
tion of the sponges from the Flagellata at 
least a tenable hypothesis, while Balfour con- 
sidered them as an intermediate group be- 
tween the Protozoa and Metazoa. 
In the last paper he published Clark com- 
pared the arguments adduced by Haeckel in 
