130° PHYLUM PORIFERA—SPON GES. 
In an extract of several sponges, Krukenberg found a 
(tryptic) digestive ferment, probably formed within the 
phagocytes, but digestion is wholly intracellular. 
Many sponges contain much pigment; thus the lipo- 
chrome pigment zoonerythrin (familiar in lobsters) is 
common. Some pigments, such as floridine, may help in 
respiration. The green pigment of the fresh-water sponge 
is closely analogous, if not identical, with chlorophyll, and 
probably renders some measure of holophytic nutrition 
possible. 
Reproduction.—If a sponge be cut into pieces, these may 
regenerate the whole—a fact which illustrates the relatively 
undifferentiated state of the sponge body. It is possible 
that fission may sometimes occur naturally. 
The frequent budding is merely a kind of continuous 
growth, but when buds are set adrift, as sometimes happens, 
we have discontinuous growth or asexual reproduction. 
In the fresh-water Spongillidze there is a peculiar mode of reproduc- 
tion by statoblasts or gemmules, A number of mesoglceal cells occur 
in a clump, some forming an internal mass, others a complex protective 
capsule, with capstan-like spicules, known as amphidiscs. According 
to W. Marshall, the life history is as follows: In autumn the sponge 
suffers from the cold and the scarcity of food, and dies away. But 
throughout the moribund parent gemniules are formed. These survive 
the winter, and in April or May they float away from the dead parent, 
and develop into new sponges. Some become short-lived males, others 
more stable females. The ova produced by the latter, and fertilised 
by spermatozoa from the former, develop into a summer generation of 
sponges, which, in turn, die away in autumn, and give rise to gemmules. 
The life history thus illustrates what is called alternation of genera- 
tions. Interpreted from a utilitarian point of view, the formation 
of gemmules is a life-saving expedient. As Professor Sollas says, 
“the gemmules serve primarily a protective purpose, ensuring the 
persistence of the race, while as a secondary function they serve for 
dispersal.” 
All sponges produce sex cells, which seem to arise from 
amoeboid mesoglcea cells retaining an embryonic character. 
In the case of the ovum, the amoeboid cell increases in 
size, and passes into a resting stage; in the case of the 
male elements, the amceboid cell divides into a spherical 
cluster of numerous minute spermatozoa. The similar 
origin of the ova and spermatozoa is of interest. Most 
sponges are unisexual, but many are hermaphrodite. In 
