The porifera and coelentera . vertheless, sponges in a state of contractionhave often been described as if they were the per-manent form, and have even been separated fromthe normal, expanded form as a distinct species,genus, or family ; while the temporary obliteration ofthe osculum or gastral cavity has been dignified by thecoinage of the terms lipostomy and lipogaMry respec-tively. Mistakes of this kind have been the cause ofgreat 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 cannotOljiithus
The porifera and coelentera . vertheless, sponges in a state of contractionhave often been described as if they were the per-manent form, and have even been separated fromthe normal, expanded form as a distinct species,genus, or family ; while the temporary obliteration ofthe osculum or gastral cavity has been dignified by thecoinage of the terms lipostomy and lipogaMry respec-tively. Mistakes of this kind have been the cause ofgreat 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 cannotOljiithus of ciathrina close up their pores and oscula at will—that is tow?traiow,,ower (after say, as a reaction to certain changes either in theHaeckei). (The oscular environment or in the internal economy. rim is not correctly re-presented ; the pores • i i should not be continued Apart from more or less rapid chanscs of up to the edt;e, but , ^ ,. „ ...^ ,-, should stop at some dis- form resulting trom contraction, we nave to. Fio. 1. tance from it.) consider a large series of form varieties which are the result of growth, and therefore of greater permanenceand importance. It has been mentioned above that the region ofattachment may grow out into a stalk, and we have therefore todistinguish, in the first place, between sessile and pedunculate is convenient to commence the discission of the variations inbody form by pointing out that almost any shape which a spongecan assume may be further complicated by the growth of a the outset the numerous form variations of sponges can beclassified into two distinct series, which start from a fundamentalmorphological difference in the mode of growth. In the first place,the primitive vase-like sponge, whether stalked or not, may retainits single osculum and gastral cavity, but become modified in formby unequal growth of the body wall. In the second i)lace, thegrowth may be such as to lead to the formation of new oscula,
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