II 8 PORIFEKA SPONGES. 



The most important fact in the life of a Sponge is that 

 which Robert Grant first observed, — that currents of water 

 pass gently in by the inhalant pores, and more forcibly 

 out by the exhalant aperture or apertures. This may be 

 demonstrated by adding powdered carmine to the water. 

 The instreaming currents of water bear dissolved air and 

 supplies of food, such as Infusorians, Diatoms, and particles 

 of organic de"bris. The outflowing current carries away 

 waste. When a sponge is fed with readily recognisable 

 substances, such as carmine or milk, and afterwards 

 sectioned, the grains or globules may be found — (a) in the 

 collared endoderm cells ; (b) in the adjacent phagocytes of 

 the mesogloea ; (c) in the phagocytes surrounding the sub- 

 dermal spaces, if these exist. It is uncertain whether the 

 epithelium of the subdermal spaces or the collared 

 endoderm is the more important area of absorption, 

 but it is certain that the phagocytes play an important 

 part in engulfing and transporting particles, in digesting 

 those which are useful, and in getting rid of the useless. 

 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 (see Chap. XXVIII.) zoonerythrin is 

 common, and, like some others, such as floridine, is regarded 

 as helping 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 Spongillidse there is a peculiar mode of reproduc- 

 tion by statoblasts or gemmules. A number of mesogloeal 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 



