THE NATURE OF SPONGES. 
171 
their tentacles like the petals of a glassy flower. Of the 
Alcyonarian group, Professor Greene observes : 64 In many, though 
not all Alcyonaria, the somatic cavities of the separate polypes 
which make up the compound mass are prolonged into canals, 
freely communicating with one another, inosculating, and form- 
ing a sort of aquiferous system, within which the nutritive 
products circulate.” 
We may now come to the first paragraph of Professor H. 
James Clark’s paper on the American Spongilla, with a hope 
that some of the difficulties which prevent its being popularly 
intelligible have been removed. He says : 44 The argument of 
Haeckel and others, that the sponges are essentially compound 
polypi, is virtually based upon the assumption that the minor 
(afferent) and major (efferent) ostioles of the former correspond 
to the mouths of the latter ; and that the profusely branching 
afferent and efferent canals of the sponges are strictly conform- 
able with similar canals in the polypidom of the Halcyonarians ; 
and, by implication, the cilia-bearing cells of the interior lining 
wall of the zoophyte find their homologies in the ciliated cell- 
like bodies of the interior chambers of the porifera. If now it 
should turn out that these last are not altogether mere cell 
components of a tissue, but are each severally an independent 
body, although closely connected with others in a common bond, 
the attempted parallelism between the two groups must utterly 
fail of confirmation. The tendency of Carter’s investigations, 
and of our own too, is to show that this is no vain supposition.” 
Professor Clark proceeds to give his reasons for believing 
that the cilia-bearing objects of the American Spongilla, on 
which he particularly writes, are a sort of individual, and not, 
as Haeckel’s theory would require, mere portions of a ciliated 
membrane. In doing this he uses terms which are unintelli- 
gible without reference to his paper entitled 44 Polarity and 
Polycephalism,” in “Silliman’s Journal” for January 1870, and 
which needs popularising for the general reader. 
Professor Clark’s endeavour in this essay was to contribute to 
the decision that meets the zoologist under various forms, What 
is an individual ? and he endeavoured to establish a new sort of 
quasi-individuality. In man, the metaphysical question of 
individuality, or personal identity, becomes so prominent from 
the dominant character of his cerebral system and the powers 
connected with it, that it requires considerable effort to con- 
template it from a purely zoological point of view. There is, 
however, no difficulty with any of the higher animals in deter- 
mining that each one is an individual in the sense of a separate 
and complete representative of the species, as soon as it is 
severed from the parental life and has an independent exist- 
ence ; but in many of the lower forms puzzling incidents occur, 
