ON THE DEVELOPMENT OF TUBULIPORA. 121 



rosive sublimate have some specific action on the substance 

 itself. The precipitate, once formed, behaves to reagents 

 quite differently from its antecedent state in solution in the 

 vesicle. Alcohol, for instance, dissolves the contents of the 

 fresh vesicles without precipitation ; but the precipitated con- 

 tents become entirely resistent to alcohol, except immediately 

 after their formation by distilled water. 



Different colonies vary a good deal in the extent to which 

 the vesicles are developed; but those obtained in the summer 

 appear to have a much greater development of the vesicles than 

 those of the same species found in the spring. I have exa- 

 mined summer specimens in preserved material only ; but in 

 many of them the excretory vesicles are very much more 

 conspicuous than in the spring colonies. Their walls become 

 very dark, and may be so thickened as to greatly diminish the 

 lumen, while the contents may appear as a single solid con- 

 cretion. The number of the vesicles may often be very greatly 

 increased in the summer. This was observed especially in 

 T. plumosa, in which summer specimens had almost the 

 entire length of the tentacle occupied by a single row of 

 closely packed vesicles. 



These facts seem to indicate that the vesicles are not nor- 

 mally discharged to the exterior, although it would not appear 

 difficult for their fluid contents to escape through the epi- 

 dermis of the tentacles. In many of my preparations ex- 

 cretory vesicles appear to have been forced to the outside of 

 the epithelia which normally cover them. I am inclined to 

 regard this as an artefact, the fluid vesicles being squeezed out 

 as the result of the contraction induced at death by the action 

 of reagents, and being precipitated outside the body by those 

 reagents. This is indicated by the fact that I have never seen 

 them on the morphologically outer side of the ectocyst of the 

 vestibules of the zooecia or of the terminal membrane of the 

 ovicell. 



The increase of the number of the vesicles in the later part 

 of the year is a reason for regarding them as excretory, and 

 this view is confirmed by their dark colour and by the con- 



