4 SPONGES 



The primitive vase -like form is retained in some instances 

 throughout life. In other cases it only occurs as a transitory 

 stage (which may even be suppressed) in the life -history, and 

 during subsequent growth it undergoes almost 

 every conceivable modification and complication 

 of form. 



In the first place, any sponge, whether of simple 

 or complex form, may under certain conditions con- 

 tract itself and close up its pores and osculum. In 

 extreme cases even the gastral cavity becomes ob- 

 literated. Such changes of form are of course only 

 of temporary duration and are of no morphological 

 or classificatory value. Sooner or later the sponge 

 expands again and passes back into its normal con- 

 dition. Nevertheless, sponges in a state of contraction 

 have often been described as if they were the per- 

 manent form, and have even been separated from 

 the normal, expanded form as a distinct species, 

 genus, or family ; while the temporary obliteration of 

 the osculum or gastral cavity has been dignified by the 

 coinage of the terms lipostomy and lipogastry respec- 

 tively. Mistakes of this kind have been the cause of 

 great confusion in the literature, and it is well, there- 

 fore, to bear in mind that many sponges are ex- 

 cessively contractile, while there are few that cannot 

 oiynthus of ciathrina close up their pores and oscula at will that is to 

 wiinlo^power (after Bay, a reaction to certain changes either in the 

 Haeckei). (The oscular environment or in the internal economy. 



rim is not correctly re- 

 presented ; the pores 



should not be continued Apart from more or less rapid changes of 



up to the edge, but , r , A . ,. J 



should stop at some dis- form resulting trom contraction, we nave to 

 consider a large series of form varieties which 

 are the result of growth, and therefore of greater permanence 

 and importance. It has been mentioned above that the region of 

 attachment may grow out into a stalk, and we have therefore to 

 distinguish, in the first place, between sessile and pedunculate forms. 

 It is convenient to commence the discussion of the variations in 

 body form by pointing out that almost any shape which a sponge 

 can assume may be further complicated by the growth of a peduncle. 

 At the outset the numerous form variations of sponges can be 

 classified into two distinct series, which start from a fundamental 

 morphological difference in the mode of growth. In the first place, 

 the primitive vase-like sponge, whether stalked or not, may retain 

 its single osculum and gastral cavity, but become modified in form 

 by unequal growth of the body wall. In the second place, the 

 growth may be such as to lead to the formation of new oscula, each 

 the vent of a separate gastral cavity. Anticipating here the theory 



