BRITISH ZOOPHYTES. 33 



ductive zooids, there are in the family Plumtilariidce, 

 what have been called guard polyps or machopolyps. 

 These are extensions of the ccenosarc lodged in nemato- 

 phores or sarcothecse, which are tubular extensions of 

 the polypary, or chambers of the walls of the calycles, 

 and serve to guard the individual polypites in some 

 way from injury, or to assist in the capture of food. 

 They have been recently discussed by Dr. R. Von 

 Lendenfold in the Ann. and Mag. of Nat. Hist, for 

 October^ 1883; but were first described by Mr. Busk 

 (Hunterian Lectures, 1857), and afterwards by Prof. 

 Allman in the A. and M. of N. H., 1864, p. 203, and in 

 his '' Gymnoblastic Hydroids/' and by Mr. Hincks, in 

 his " British Hydroid Zoophytes.'' 



Dr. Metschnikoff (Q. J. M. S., xxiv. 91, 92) considers 

 that "the chief function of these orders is prophylactic, 

 and that they eat up the necrotic parts of the colony, 

 and continually explore the organs in their vicinity in 

 order to render harmless, by devouring them, any in- 

 jurious bodies that may be present.'' He shows that 

 the contents of the sarcothecce are capable of extending 

 themselves into the neighbouring calycles, and by a 

 process of intra-cellular digestion absorbing any dead 

 hydranths that may be there. 



' It only now remains to notice the quality of phospho- 

 rescence possessed by many of the Hydroida, both in their 

 complete and in their medusoid states. The immense 

 numbers of fixed and free zooids which are contained in 

 the neighbourhood of our shores, are amply sufficient to 

 account for the phosphorescent appearance of the sea: — 



" Soft, brilliant, tender, through the wave they flow, 

 And make the moonbeams brighten where they glow." 



Mr. Gosse describes the beauty of this phospho- 



