ALL.MAn's GYMXOrsL.VSTIC HYDP.OIDS. 67 



may not in reality be more extensively present than is 

 commonly supposed. 



2. With regard to the muscular or motile fibrilla?, notwith- 

 standing what has been done, some conflict of opinion still 

 appears to exist, This may, perhaps, in part arise from 

 tliere being two kinds of fibrillated contractile tissue in the 

 hydroida, viz. that noticed by Professor AUman (p. 11:2), 

 and described as consisting of tubular fibres, about ^-J^^yth of 

 an inch in diameter, smooth and nucleated, and often pre- 

 senting the aspect of fusiform cells, and so fiir not unlike the 

 involuntary muscular fibre of higher animals, which form of 

 contractile fibres would seem to be present more especially in 

 the tentacles and bodies of certain hijclranths. And besides 

 this, another form of fibrillated tissue, apparently widely 

 different from the above, found in the umbrella and velum 

 of the medusidae, consisting, as stated by the author (p. 1 14), of 

 fibres having a diameter of not more than-^^ 1,-;^ th inch, and 

 resolvable under a high power into a singleseriesof corpuscles," 

 and thus presenting a marked resemblance to the ultimate 

 fibrillse of striated muscle, spread out so as to formabroad mem- 

 branous expansion. This is the only kind of muscular tissue 

 that has fallen under our own observation, although the 

 distinctness of the striation varies much in different cases. 



3. The presence or absence of a distinct nervous system 

 is also a point with respect to which we still are very much 

 in want of definite knowledge. 



The existence of such a system in the Beroidce seems to 

 have been tolerably satisfactorily made out. What has been 

 so regarded in the steganophthalmatous medusae is, as it 

 seems to us, of extremely doubtful nature. And although 

 many excellent observers, and especially Haeckel, one of the 

 latest who has written on this subject, appear to have arrived 

 at the conclusion that traces of such a system are observable 

 in the gymnophthalmata, the question can by no means be 

 regarded as finally settled. 



In the last chapter of the present Part we have a general 

 account of the process, or rather processes, of reproduction in 

 the hydroida ; but into this subject we have at present no 

 space to enter further. 



In conclusion, we must congratulate the Ray Society that 

 such a work as the present should have been brought out 

 under their auspices. As regards the beauty and fidelity of 

 the figures it is impossible to speak too highly, and the 

 admirable way in which the plates have been executed is 

 beyond all praise. The Avork, when completed, will mark an 

 epoch not only in the history of the Ray Society, but in the 

 zoological literature of Europe. 



