A NEW FIELD FOR THE MICROSCOPIST. 
125 
this enlarged amoeboid body now gives origin to a structure so 
closely resembling the 44 morula ” that results from the primary 
segmentation of the ovum of all higher animals, that the nature 
of a true egg or ovum has been inaccurately attached to it by 
some authorities. By degrees each constituent segment of this 
moruloid body assumes a lengthened conical form, and, acquir- 
ing a terminal flagellum, presents in the aggregate the aspect 
given at Plate III. fig. 27. 
Developing still further, this moruloid body finally, and in 
its most characteristic phase, exhibits the form shown at fig. 28 
of the same plate, and in which condition it may be described 
as a spherical or ovoid aggregation, hollow within, of typical 
collar-bearing monads or spongozoa, individually identical with 
those of Codosiga pulcherrima or any of the independent collar- 
bearing types figured on the same plate. Floating away in 
this condition the collars and flagella of the sponge-monads are 
subsequently retracted, a syncytial exudation is thrown out 
as a veil around them, the spicules or other skeletal elements 
make their appearance in the same, and the body, attaching 
itself by some point of its periphery, usually the posterior one, 
speedily presents in miniature all the essential features of the 
parent sponge which gave it birth. The special collar-bearing 
cells now project into the interior cavity, opening externally by 
a single flue or osculum, and rapidly multiply by those various 
processes of fission or resolution into spores already described. 
By those hitherto insisting on the recognition of sponges as 
animals qualified to rank with the Coelenterata or lowest Metazoa 
rather than with simple unicellar Protozoa, the free-swimming 
compound gemmules just discussed have been seized upon as 
yielding the most conclusive evidence. The various arguments, 
however, brought forward in association with these structures in 
support of this coelenterate view, have been considerably weakened 
since the first attempt made by Prof. Haeckel to establish for 
them a form and structure identical with his typical but hypo- 
thetical 44 Grastraea,” or larval stockform of all animals higher 
than the Protozoa. This 44 Gastraea,” consisting of a capsular 
body with a single terminal orifice and body-wall composed of 
two separate cellular membranes, an ectoderm and endoderm, was 
supposed to find its ideal personification in the compound ciliated 
sponge-gemmule. A more intimate and accurate acquaintance 
with these bodies has, however, revealed to numerous observers 
the entire untenability of this hypothesis. It is now definitely 
determined that there is no separation of the walls of the gem- 
mule into an outer and inner cellular membrane or ectoderm, as 
originally premised, and no terminal orifice leading into the 
central cavity. The strongest, and apparently the only argu- 
ment, indeed, that can now be brought forward in favour of the 
