ON THE DEVELOPMENT OF TCTBULIPORA. 119 



langea are dissolved by strong ammonia, by 4 ])er cent, 

 potash, by 90 per cent, alcohol, and by nitric acid. Osmic acid 

 also destroys them. 



They are not affected by corrosive sublimate, nor are they 

 broken up by acetic acid. After being fixed with corrosive 

 sublimate, they are no longer affected by osmic acid, nor by 

 distilled water. 



On adding distilled water the fresh compound vesicles lost 

 the boundaries of their constituent vesicles, and turned a 

 diffuse red-purple, that colour becoming soon restricted to 

 numerous granules, which disappeared on adding ammonia. 

 The homogeneous vesicles of the terminal membrane were 

 precipitated by distilled water; some of these (probably the 

 more delicate ones) were dissolved by ammonia, while others 

 remained and turned purple inside. 



Several facts in the above experiments suggest that there is 

 some connection between the well-known purple colour of 

 certain species of Tubulipora and the homogeneous or com- 

 pound vesicles. Tiie change from a greenish to a purplish 

 colour was specially marked ou adding distilled water to the 

 compound vesicles, and it also occurred in the homogeneous 

 vesicles, under certain circumstances, as the result of treat- 

 ment with ammonia or potash. The purple colour is, how- 

 ever, not entirely due to the action of reagents. The branches 

 of T. liliacea, for instance, are commonly purple during life, 

 the colour occurring as a purple pigment in the cells of the 

 terminal membrane, as correctly stated by Smitt (39, p. 22), 

 and in other parts. This purple pigment was not affected by 

 the successive action of distilled water, ammonia, and potash, 

 nor by acetic acid. 



It seems to me probable, however, that the purple colour 

 often seen in dry preparations of species of Tubulipora may 

 in many cases be due to post-mortem changes of the excre- 

 tory vesicles. This view was confirmed by an observation on 

 a colony of T. liliacea which, when alive, had no trace of 

 purple, but assumed that colour after being washed with fresh 

 water and dried. The colour is not seen in colonies preserved 



