122 SIDNEY F. HARMER. 



cretion-like contents which may appear within them. Their 

 occurrence in the terminal membranes of buds (even of young 

 ones) as well as of the polypides and ovicells might suggest 

 the view that they were nutritive. 



Davenport (7, pp. 34—, pi. vi, figs. 54, 56, 57, 59) has 

 described certain mesoderm cells (which have also been ob- 

 served by Braem) in the budding regions of Paludicella. 

 These contain refractive bodies which are not altogether unlike 

 the vesicles which I have described above, and they are re- 

 garded by both Braem and Davenport as nutritive. It appears 

 to me that these bodies are not comparable with the vesicles 

 of Tubulipora; but there is enough appearance of similarity 

 to make it worth while to call attention to the resemblance. 



I can hardly doubt, however, that the Tubulipora vesicles 

 have a close similarity to the " Exkretblaschen" which have 

 been described by Eisig (8, pp. 725 — ) in Capitellidse. The 

 reactions of these bodies, and particularly the resistent way 

 in which some of them behaved to mineral acids and potash, 

 led Eisig to the belief that they contained chitin as one of 

 their constituents, and that this substance was to be regarded 

 as one of the normal nitrogenous excreta. The reactions 

 which I have described agree so well with Eisig's results that 

 the view that the vesicles are of an excretory nature appears 

 to me to be greatly strengthened thereby. If the insoluble 

 substance which is precipitated by various reagents is really 

 chitin, or some similar body, the normal homogeneous vesicles 

 may perhaps be considered to contain a substance which could 

 be called chitinogen, which, though itself soluble, readily 

 passes into an insoluble state. The vesicles might conceivably 

 be employed in giving rise to the chitinous parts of the ter- 

 minal membranes or vestibules of the zooecia, although their 

 number would appear disproportionately large on this hypo- 

 thesis. It is perhaps more likely that their occurrence 

 in the tentacles and terminal membranes is due to a ten- 

 dency to deposit the excretory substances in the peripheral 

 parts of the colony, and to the advantage of removing waste 

 products of metabolism from the polypide-buds and embryo- 



