and Physiology of the Spongida. 35 



Observations. 



It is not intended that this Table should be considered com- 

 plete even for all the known forms of the flesh-spicule ; but it 

 may aid the memory in retaining an acquaintance with most 

 of them ; and as with the Table before given of the " known 

 forms " that may be assumed by the skeleton-spicule, so here, 

 also, this may aid the student in describing new ones of the 

 flesh-spicule. 



Specific Value of the Flesh- Spicule. 



A few remarks here are necessary as regards the specific 

 value of the flesh-spicule, since, as the same form of skeleton- 

 spicule is often found among the normal spicule-complement 

 of different species of the Spongida, or with such slight and 

 almost inappreciable differences that they are of no use speci- 

 fically, so it is with the flesh-spicule. 



Although the navicular or shuttle form of the equianchorate 

 and the simple minute bihamate are common to several very 

 different kinds "of sponges, there is no form so common or so 

 diversified, perhaps, as the tricurvate or bow-shaped spicule, 

 which in many instances is a simple minute acerate so like 

 the skeleton-spicule that it might be easily mistaken for a 

 young form of the latter. 



It is under this form that the tricurvate often appears in 

 sheaf-shaped bundles, each bundle of which is developed in a 

 separate cell (see "Mother Cell of the Spicule," 'Annals,' 

 1874, vol. xiv. p. 100, pi. x. figs. 3-9), and so numerous in 

 some instances that it would appear to afford a characteristic 

 feature, if it did not so happen that the sheaf-shaped bundle 

 is common to so many totally different kinds of sponges. It is 

 therefore desirable to remember that this is the tricurvate 

 spicule which, after the bundles have been eliminated from the 

 mother cell into the structure of the sponge generally, may 

 attain a somewhat more recognizably tricurvate form. 



It is also desirable to notice that sponges are often densely 

 charged with minute transparent globules, which have such a 

 siliceous aspect that, if it were not knoAvn that the Hypho- 

 mycetous Fungi (Mucor and Botrytis) sooner or later destroy 

 the whole of the sarcode, or soft parts of the sponge, under the 

 least humidity, and thus fill it with their sporules, these little 

 transparent bodies might be taken for a part of the spicule- 

 complement of the sponge. If, however, there should be any 

 doubt on the subject, and the parent filaments or mycelium ot 

 the fungus be not observed, the doubt may be got rid of by 



3* 



