A NEW FIELD FOR THE HICROSCOPIST. 
121 
collar-bearing species, simultaneously announced his discovery 
that one of the calcareous-spiculed sponges ( Leucosolenia 
botryoides , Bwbk.) consisted of aggregations of essentially similar 
collar-bearing monads, immersed within the structureless sarcode 
or spicule-producing element. This important discovery, con- 
firmed by an examination of other species, Prof. Clark regarded 
as completely setting at rest the long-vexed question concerning 
the true nature and affinity of the sponges, and conclusively 
demonstratingthe necessity of their recognition as colony- building 
flagellate infusorial forms. Professor Clark’s decease shortly after 
this announcement, together with the novel theory concerning 
these same organisms that was brought forward at about the 
same date by Professor Ernst Haeckel, and in which it was 
sought to show that the sponges were referable to a far more 
highly organized animal group, served to almost entirely divert 
the attention of biologists from those views that originated with 
the first-named authority. Notwithstanding, however, this tem- 
porary diversion of scientific thought into a novel, and, at first 
sight, sufficiently plausible channel, the researches of recent 
investigators are tending to confirm the views of the American 
naturalist, almost all of these being unanimous in recognizing 
that the ciliated lining of the various-shaped sponge-cavities 
is -essentially composed of collar-bearing flagellate cells similar 
to those just described as existing in Leucosolenia botryoides. 
Although thus admitted, however, by such authorities to consti- 
tute an important element in all sponge-structures, very few are 
at present inclined to concede to these collar-bearing flagellate 
cells the primary position assigned to them by Professor Clark. 
In accordance with the view of the former, indeed, each such 
flagellate collar-bearing cell is not to be regarded as a separate 
and independent monad or individual, but merely as a single 
cell-constituent of a continuous and epithelium-like internal 
lining membrane. 
The above-mentioned opposing views held respecting the true 
nature and affinity of the sponges may thus at the present day 
be said to provide material for as fierce a controversy between 
leading scientific authorities as was maintained in similar circles 
during the first half of this century relative to the claims of 
these same organisms for admission into the ranks of the 
animal kingdom, and which has not for so very long a while 
been universally accorded them. If, as Prof. Haeckel and the 
advocates in whole or in part of his theory assert, sponges are 
composed of separate multicellular membranes or tissues, they 
undoubtedly find their nearest allies among the Ccelenterata, 
including the sea-anemones and h} droid zoophytes. If, on the 
other hand, as represented by Prof. Clark, they consist of aggre- 
gations of unicellular collar-bearing flagellate monads, their 
