28 



Monograph of Prof. E. Forbes, is not very satisfactory, as that emi- 

 nent observer does not appeal* to have noticed their peculiar structure, 

 as detailed by Will, and as described in the foregoing paper. He says 

 (I. c. p. 8) that " the otolitic vesicle, which from analogy and its pecu- 

 liar structure, is considered an organ of hearing, is a small spherical 

 sac, developed in the midst of the granular substance of the bulb 

 [of the tentacles] and containing more or fewer vibrating bodies." He 

 then proceeds to give Will's description of the marginal vesicle in 

 Geryonia ; overlooking, apparently, the fact that the writer both de- 

 scribes and figures these vesicles, in that species at least, as quite 

 distinct from the tentacular bulbs ; and, moreover, that Will re- 

 peatedly denies that he ever observed any vibratory motion in their 

 contents. Neither does Will nor Milne-Edwards anywhere describe 

 these bodies as developed in the midst of the granular substance of 

 the bulb; for in cases, such for instance as Cytceis polystyla and 

 Thaumantias leucostyla, described by the former writer, where the 

 marginal vesicles are placed, not intermediate to the tentacles, but 

 beneath or covered by their bases, still they are said to be " immedi- 

 ately beneath the cuticle." 



It would have been strange, however, had not such an accurate 

 and close observer as Prof. E. Forbes, noticed these bodies at all. 

 Such is not the case ; although he does not appear to have paid 

 any very close attention to them. In the description of Thaumantias 

 globosa (p. 46) it is said, " here and there among the tentacles are 

 little colourless tubercles studding the margin ;" and in that of T. 

 inconspicua, which is not improbably the species I am describing, it 

 is noticed, that " between each pair [of tentacles] there is a rudimen- 

 tary marginal tubercle." AVith respect to Thaumantias quadrata, 

 Prof. E. Forbes notices and figures (Plate IX. fig. 2 c), what I presume 

 to be the marginal bodies, as " intermediate bulbs," from which it 

 might almost be presumed that he looked upon them as incipient 

 tentacular bulbs. In the figures also of 



Thaumantias octona, Plate VIII. fig. 4 b and 4 e. 



Thaumantias maculata, Plate IX. fig. 4 e. 



Thaumantias globosa, Plate X. fig. 4 g. 



Thaumantias inconspicua, Plate VIII. fig. 3. 



Modeeria formosa, Plate VII. fig. 1 /. 



Oceania turrita, Plate II. fig. 2 c and d. 



Oceania episcopalis, Plate II. fig. 1 b. 



Oceania octona, Plate II. fig. 3 b and c. 

 Are represented what I conceive to be the marginal corpuscles, but 



