ON THE DEVELOPMENT OP TUBULIPORA. 115 



Devonshire, the tentacles of T. pluraosa normally contain 

 these vesicles, and those of T. liliacea and T. phalangea 

 do not normally contain them. 



I spent some time at the Plymouth Laboratory during the 

 spring, for the purpose of endeavouring to decide the nature of 

 these vesicles. Material was unfortunately not plentiful, but 

 some results were obtained. The most convenient w^ay of 

 studying the vesicles was to dissect out the fresh polypides of 

 T. plumosa, and after separating the tentacles from one 

 another to examine them in sea water. Although there is 

 some difficulty in dissecting out the polypides, decalcification 

 cannot well be employed, because the vesicles are at first 

 readily altered by reagents. 



The vesicles of T. plumosa do not occur in the lumen of 

 the tentacles, as might at first be supposed ; but they are 

 situated in the external epithelium on the abaxial side of the 

 lumen (fig. 26). In specimens obtained in the early spring 

 no trace is seen, in fresh material, of the typical vesicles found 

 in sections, but the epithelium contains a row of greenish 

 refractive vesicles, which are commonest near the tips of the 

 tentacles, but may also occur more proximally. These vesicles 

 are not bounded by any distinct membrane, but appear rather 

 as drops of a fluid substance contained in the epithelium. 

 Other smaller granules of yellowish pigment (/>.) occur here 

 and there in the epithelial cells, but these have a more solid 

 appearance, and are not aff'ected by reagents in the way 

 characteristic of the larger vesicles. 



In sections, on the contrary, the vesicles appear to be 

 bounded by a sharply defined membrane ; and it was therefore 

 necessary to consider whether they might be symbiotic Algae. 

 With the view of testing for starch and cellulose, I added a 

 solution of iodine in potassium iodide to the fresh tentacles, 

 with somewhat surprising results. The vesicles, which were 

 at first more or less irregular in outline, immediately rounded 

 themselves ofi'and became darker in colour, an active Brownian 

 movement at once becoming apparent in their interior (show- 

 ing that they are really fiuid). This lasted for a brief period, 



