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POPULAR SCIENCE REVIEW. 
affinity of the sponges with the Coelenterata or other Metazoa, 
is the circumstance that these free-swimming gemmules are 
produced, as already notified, by a process of cleavage or segmen- 
tation resembling that usually regarded as the special property 
only of the true ovum of all higher animals, from the Coelen- 
terata upwards. Could no instance he adduced in which parallel 
phenomena occur among other undoubted Protozoa, this argu- 
ment would carry with it considerable weight. It has, however, 
been recently shown by the valuable researches of Messrs. Dal- 
linger and Drysdale that, among certain simple free-swimming 
monad forms, the coalescence of two or more individuals may give 
rise to a precisely similar process of cleavage or segmentation, ter- 
minating in a similar moruloid structure. The component seg- 
ments of this pseudo-morula, however, are the equivalents, as in 
the case of the sponge-gemmule, of distinct individual zooids, 
and which in this instance become finally separated from one 
another and distributed through the surrounding water as uni- 
flagellate monads.* It requires merely the permanent attachment 
in a colony-form of the individual units of Messrs. Dallinger and 
Drysdale’s multiple-fission monad to produce a structure in all 
ways corresponding with the ciliated sponge-gemmule in its 
earliest stage, as shown at Plate III. fig. 2 7, and the addition to the 
same units in such an attached form of terminal hyaline collars, to 
typify the still more characteristic phase illustrated at fig. 28. 
The close relationship which undoubtedly subsists between 
the sponges and the, as now shown, extensive group of indepen- 
dent collar-bearing Flagellate Protozoa represented in luxuriant 
variety in the accompanying plates, will scarcely be called in 
question by those who, first making themselves acquainted with 
the members of this last-named group, turn their attention to . j 
the physiology of the sponges. It is only, indeed, through such 
a preliminary acquaintance with the more simple independent 
forms that this intricate question of the nature and affinities of 
these more complicated aggregations of otherwise essentially 
similar units can be satisfactorily approached. While, there- 
fore, recommending the newly-discovered group of independent 
collar-bearing Flagellate Protozoa to the attention of working 
microscopists, it is much to be desired that they shall supple- 
ment such observations as they may make in connection with 
the same by a practical examination of the structure of all such 
sponge forms in the living state to which they may have access. 
In either field our knowledge may be said as yet to extend no 
further than the threshold, and in each of the same there is pro- 
• An illustration of this interesting type will be found in vol. xiv. 
Plate CXXIV., figs. 9 and 11, accompanying the article quoted in the 
footnote of page 115. 
