86 ZOOPHYTA HYDROIDA. 



deciduous parts, but on the general fleshy substance of the 



body."* 



The polypes are placed in the cells within which, with the 



exception of the Tubularise, they can hide themselves entirely 



when danger threatens. When at rest and in their native sites, 



they expand their tentacula and push them far beyond the rim 



of their cups, in readiness to arrest any small worm or crusta- 



ceous insect which may float within their circle. 



" Utque sub sequoribus deprensum polypus hostem 

 " Contiiiet, ex omni dimissis parte ilagellis." 



Ovid. Met. vi. 366. 



These tentacula are always simple but roughish, (Fig. 9 c,) and 

 in the centre of the disk round which they are arranged we perceive 

 the oral aperture (d,) leading to a stomachical cavity without 

 intestine or other chylopoetick viscus. The body is somewhat 

 globular, soft and irritable ; and it is prolonged posteriorly down 

 the stalk or tube to be united with the central pulp which fills 

 the branches and stem, (e,) so that in this manner all the po- 

 lypes of the same polypidom are connected together by a living 

 thread, and constitute a family whose objects and interests are 

 identical, and whose workings are all regulated by one harmo- 

 nious instinct. 



" Unconscious, not unworthy, instruments, 



By which a hand invisible was rearing 



A new creation in the secret deep." 

 Or if, with Linnaeus and Cuvier, we suppose that the " whole 

 composure makes one animal," this may be described as a sort 

 of hydra divided, after the manner of a tree, into many or in- 

 numerable branches, from each of which pullulate one or more 

 armed heads to capture and digest the prey that is to serve for 

 the nutriment of their common trunk. 



The reproductive gemmules of Tubularia and Coryne are 

 generated in the interior and extruded near the base of the ten- 

 tacula ; but in all the other genera they are produced in exter- 

 nal vesicles, which were therefore appropriately named by Ellis 

 the matrices or ovaries, and which we have already mentioned 

 as being larger than the cells and irregular in their distribution. 

 They are produced at certain seasons only, most commonly in 

 spring, and fall off" after the maturity and discharge of their con- 



* Grant's Outlines of Comp. Anatomy, p. 14. 



