116 SIDNEY F. HARMER. 



at the end of which (fig. 27) each of the homogeneous greenish 

 vesicles took on the appearance of the sharply contoured 

 spherical bodies seen in sections, a certain number of brownish 

 granules being precipitated in their interior, and usually coming 

 to rest on the inside of the wall of the vesicle, the fluid con- 

 tents of which are now colourless.^ The subsequent addition 

 of strong sulphuric acid gave no blue colour, and did not 

 greatly alter the vesicles. These changes took place in the 

 same way in vesicles which had been freed from the polypides 

 during the dissection. 



The greenish vesicles were found in the fresh material in 

 the tentacles (in T. plumosa alone) and beneath the terminal 

 membranes, i. e. in precisely the same places as those in which 

 they had been previously noticed in sections. 



The above-described reaction was due to the iodine and not 

 to the potassic iodide. This was shown by the fact that a 

 solution of potassic iodide (a) in distilled water, (b) in sea 

 water, was added to other specimens without producing any 

 effect. On adding a fragment of iodine to either solution the 

 characteristic precipitation at once took place. The same 

 result was produced by adding sea water in which a fragment 

 of iodine had been rubbed up. 



It soon became apparent, however, that iodine was not alone 

 in precipitating the contents of the homogeneous vesicles. 

 The same result was produced by the following reagents : — 

 distilled water, solution of corrosive sublimate (in fresh water 

 or sea water), strong ammonia, osmic acid. 



The darker (browner) colour assumed by the vesicles in the 

 first experiment is not merely the eflect of staining by the 

 iodine, since it occurs with other reagents, even with distilled 

 water. In all cases the colour of the homogeneous vesicle at 

 once becomes darker, and an appreciable interval occurs 

 during which nothing else can be made out. The Brownian 

 movement then commences, the granules being at first invisible 

 individually. The vesicle soon contains numerous minute 



1 The vesicles are very similar to those which have been figured by Durham 

 ('Quart. Journ. Mic. Sci.,' xxxiii, pi. 1, fig. 3) in Spatangids. 



