44 



GUIDE TO THE COEAL GALLERY. 



Fig. 5. 



Case 3, tentacles at the base and scattered knobbed tentacles above. The 



two kinds of tentacles can be clearly seen in this specimen with the 

 aid of a simple lens. 



Hydractinia echinata* (Figs. 8, 9) is always found forming a white 

 fleecy covering on univalve shells inhabited by Hermit Crabs. " The 

 waving forest of tall and graceful polypites generally reaches its 

 greatest height towards the mouth (of the shell), round the edge of 



which are set the curious snake- 

 like appendages. Intermingling 

 with the perfect polypites are the 

 rudimentary zooids, which carry 

 the generative sacs, attenuated by 

 their work and looking as if 

 weighed down by their burden" 

 (Hincks). The polyps rise from a 

 chitinous crust covered with conical 

 serrated spines. 



Monocauliis imijerator * (Fig. 

 10), one of the most remarkable 

 acquisitions of the ChaJlenger Expe- 

 dition, was obtained from depths 

 of 1,875 and 2,900 fathoms in 

 the North Pacific. A naked stem 

 over seven feet in length, and 

 bulbous at the lower end, is sur- 

 mounted by a large polyp with 

 basal and oral circles of filiform 

 tentacles. The polyp was pale 



(loniitudiual section); B, of a Hy- Pi^^k, and measured nme mches m 



droid Medusa, o, mouth ; g, gastric breadth across the expanded basal 



cavity; «, tentacle; s?, structureless • . . tpntaolps Tlie exhibited 



lamella; g', jelly between ectoderm ^^^^^^ ^I tentacles. xne exniOlteti 



and endoderm ; rk, radial canal ; specimen (Case 3) is sadly altered 

 ^, velum ;W/.- circular canal. (From f^.^j^ ^^.j^.-^l- |,. ^^^g |^ YlIq; but, as 

 Lang s Text-book ComiJ. Anat. J 



Sir AVyville Thompson observed, 



" these delicate things, drawn up rapidly through the water from a 



depth of four statute miles, suffer greatly from this violent change." 



The specimens almost seemed to melt away, and had to be 

 promptly put into alcohol, which has hardened and contracted them 

 to their present condition. 



Cordylopltora lacustris* is* a fresh-water Hydroid, with branches 

 rising from a creeping stolon to a height of two or three inches ; 



A. Din gram of a Hydroid feeding polyp 



