HYPURGON SKEATI. 733 



boiling microtome sections of the colony in sulphuric acid, 

 may still be mounted whole after this treatment. Boiling in 

 aqua regia and boiling in fuming nitric acid are equally 

 ineffectual in disintegrating the pellets; when these latter 

 reagents are used the test naturally forms part of the residue^ 

 since they are not capable of dissolving tunicin. 



When isolated by means of sulphuric acid the pellets have 

 a black colour, due to the action of the acid on the organic 

 matter contained in them. These blackened pellets may next 

 be washed and calcined, and though raised repeatedly to 

 cherry heat they still remain intact, and are now opaqvie 

 white when examined by reflected light. Mounted in oil, or 

 passed through oil into balsam, they become transparent. 

 Calcined pellets dissolve completely in hydrofluoric acid. 

 Prolonged boiling in a strong solution (nearly saturated) of 

 caustic soda resulted in the dissolution of calcined pellets. 



It seems, then, that the strong coherence of the pellets must 

 be due either (1) solely to cohesion and adhesion between the 

 foreign particles contained in them, or (2) to a deposition of 

 silica between these particles. The siliceous nature of the 

 greater part of this foreign matter makes it impossible to 

 determine between these two alternatives. It naturally 

 suggests itself that this property of coherence of the pellets 

 is an adaptation to enable the animal to utilise waste organic 

 matter with impunity. But it must be mentioned that the 

 pellets are porous, taking stains readily both before the 

 treatment described above, and also at every stage during it. 



It is curious that the pellets are also highly fragile; they 

 crumble at once under pressure of the cover-slip. 



Melicerta tubes were boiled in acid for conqoarison : the 

 form of the component pellets was lost almost immediately — 

 as soon as the cementing substance between neighbouring 

 pellets disappeared. 



A parasitic crustacean was found in one ascidiozoid, 

 occupying a large part of its branchial chamber. The body 

 of the parasite is a mere sac filled with ova in an advanced 

 state of segmentation. There appear to be six pairs of 



VOL. 40, PART 4. NKW SERIKS. 13 B Ij 



