18 Spong. 
SPONGE. 
rounded cells. When the larva is fixed the ciliated cells lose their cilia, 
and occupy a peripheral zone under the ectoderm. The large rounded 
cells iu the interior now become amoeboid, and, sending out pseudopodia, 
capture the former ciliated cells one by one. Each cell, when captured, 
is incorporated. When the capture is complete, the larva appears spread 
out and filled with the large cells, which are now perfectly round, and 
show round their own nucleus a number of little nuclei, which Maas and 
Gotte took for vitelline granules. After 24 to 36 hours the captured 
cells become active, travel to the periphery of the large cell, and emerge 
from it. Some form the lining of canals, others become grouped in 
little hollow masses, acquire collars and flagella, and become ciliated 
chambers. The pores and oscula are distinct from their origin. In 
Aplysilla the formation of the ectoderm and chambers is similar to that 
in Spoug ilia. 
The capture of the ciliated cells is a phenomenon of phagocytosis, 
which is incomplete in that it is temporary, though a certain number 
appear to be really digested. It resembles the histolysis of insects, with 
the difference that here the elements incorporated by tho phagocytes are 
utilized in the subsequent histogeny directly, and not as simple nutritive 
matter. 
For descriptions aud figures of the larva of Esperella sordida , Bwk., 
see Hanjtscjh, pp. 215 & 216, pi. xi, figs. 8 & 1). 
Wilson describes the gemmule development of Esperella fibrexilis , n. sp., 
and Tedania brucei , n. sp., to which are added observations on the egg 
development of Tedanione fcetkla and Ilircmia acuta. The mesoderm of 
Esperella contains certain cells, distinguished by their size, which con- 
gregate into groups, forming gemmules. The outermost cell layer of 
the gemmule becomes flattened, forming a follicle. The gemmules 
increase in sizo by cell growth aud division, and by fission of neighbour- 
ing small gemmules. It is possible that some gemmules originate from 
single cells. The ripe gemmule is made up of closely-packed cells, filled 
with yolk granules, with indistinct cell boundaries. It lies in one of the 
larger canals, suspended by threads of tissue, binding the follicle to the 
canal wall. It next goes through a process, analogous to segmentation, 
by which tho solid gemmulo is split up into smaller and smaller masses 
of cells, and finally into its constituent cells. The outermost layer forms 
a flattened ectoderm, enclosing amoeboid cells, connected by processes 
and separated by fluid. The ectoderm next becomes columnar aud 
ciliated, except at one pole, where it remains flat. The inner cells at this 
pole become closely appressed, forming a mass of polygonal cells, in 
which spicules are formed. In this condition the embryo swims out free 
from an osculum. Before fixing the ectoderm begins to flatten, from the 
non-ciliated spicular pole backwards. While there is still a remnant of 
ciliated epithelium, the larva fixes by the spicular pole, but obliquely, 
and becomes a thin flat mass. The subdermal cavities and the canals 
appear as lacunm, which open into one another, and to tho exterior by 
perforation of the intermediate tissue. Pores and oscula are at first 
