440 Proceedings of the Eoyal Physical Society. 



which runs beneath the insertion of the lower rim of ten- 

 tacles. The zoophyte has the power of changing its place. 



Description of Plate XVII. (Vorticlava proteus .) 

 Fig. 1. — Vorticlava Proteus contracted. 

 Figs. 2, 3, 4, 5. — Same in different states of extension. 



Fig. 6. — Diagram of the tissues of the polyp of V. Proteus ; a a', colletoderm 

 attached to subtentacular ridge b ; c, ectoderm ; d, endoderm. 



(2.) Trichydra pudica. (Plate XXII.) 



This hydroid, which I have already described to the 

 Society, was found completely covering a small shell from 

 the " Fluke Hole." As its mode of reproduction has never 

 been observed, I placed it in a small vessel of carefully-ex- 

 amined sea-water, and exposed it to light, a mode of treat- 

 ment which often induces the Hydroidae to assume their 

 medusoid phase. After some time, two small medusoids 

 were found in the water, but I was unable, by the most care- 

 ful examination, to detect their mode of development, as no 

 " gonophores" appeared on any part of the coenosarc. The 

 connection of these medusoids with Trichydra is yet open 

 to doubt, although I am convinced that no other zoophyte 

 occurred on the shell, or in the water in which it was placed. 



Medusoid of Trichydra pudica f — Umbrella mitre-shaped, 

 covered with minute thread-cells. Sub-umbrella with four 

 lateral canals, destitute of ovaries or sperm sacs. Peduncle 

 short, cylindrical, four cleft at the mouth. Tentacles four, 

 short, with two or four intervening tubercles. Oolites 

 absent, eye-specks absent. 



Description of Plate XXII. (Trichydra pudica.) 

 Fig. 1. — Polyp extended, showing the lax habit of the zoophyte. 

 Fig. 2. — Polyp withdrawing itself when disturbed. 

 Fig. 3.— Young Polyp. 

 Fig. 4. — Polyp within its tube. 

 Fig. 5. — Empty cell. 

 Fig. 6. — Supposed medusoid. 



(3 ) On the Development o/Pycnogon Larvoe within the Polyps of 

 Hydractinia echinata. 



In a communication made by Professor Allman to the 

 British Association in 1859, entitled, "On a remarkable 

 form of Parasitism among the Pycnogonidce" the author de- 



