Chap, xiii.] REPRODUCTION OF SPONGES. 483 



may be call the male proiiucleus. Approaching 

 the female pronucleus it gradually fuses with it, and 

 thereby gives rise to a fresh structure, the so-called 

 segmentation nucleus. 



Pausing for a moment to consider how far the 

 history now detailed has led us, we find that there has 

 been a fusion of cells which, although different in 

 final form, have arisen from parts which at first were 

 exactly similar. 



In the lowest forms the generative cells are not 

 aggregated into any special masses, and though we 

 can say that here there are male and there female 

 cells, we cannot with accuracy speak either of testes 

 or of ovaria ; here, as with various other organs, we 

 find a diffused preceding a localised or concentrated 

 arrangement. 



The Sponges afford an example of this, the 

 reproductive cells being, as a rule, scattered through 

 the mesoderm (see Fig. 53, page 106) ; to this state- 

 ment Myxospongia and Euspongia form exceptions ; 

 in the latter the ova are arranged in small groups, are 

 embedded in connective tissue, and hold a definite 

 topographical relation to the afferent canals. Here, 

 too, the ova are naked and amoeboid, and not yet 

 enclosed in a distinct membrane, as they are in most 

 of the higher Metazoa. 



Asexual reproduction does obtain so far among 

 the sponges that buds may be given off from an 

 individual, and an increase in a sponge colony can be 

 effected in a way which is of some commercial impor- 

 tance. The method here referred to has been tried in 

 the Mediterranean, and in the Florida sponge fishery 

 with a certain measure of success, the greater com- 

 pleteness of which does not appear to depend on the 

 sponge as much as on suitable fishery legislation. A 

 piece of sponge, some two or three inches high, is 

 carefully cut off from the rest of the mass ; owing, as 



