of Mollusks in Holothurise. Ill 



vascular system of a Holothuria is not an organ of the Holothuria, 

 and the allantois is not an organ of the mammalian foetus. 



As for the Medusa? and Polypes being distinct classes of the 

 animal kingdom in any sense in which the word class can be 

 applied to mollusks and Holothuria, zoologists have been so long 

 agreed, that it seems hardly worth while to have raised the 

 question. 



A considerable amount of new matter is added by Prof. Miiller 

 with respect to the possible sexual development of Medusae, from 

 Medusse which have proceeded from Polypes, but our space will 

 not permit us to enter upon that subject. One observation only 

 we would make, namely, that supposing Prof. Muller's hypo- 

 thetical, most favourable case, to be discovered, i. e. the sexual 

 development of a Sarsia or the like, from a Sarsia, there would 

 not be the slightest analogy with the supposed process in Synapta. 

 To have a parallel case, not only must we find a Sarsia sexually 

 propagated from a Sarsia, but we must find Polype-producing 

 sexual organs upon the Polype whence the Sarsia has proceeded. 

 There is not at present the slightest evidence that such a case as 

 this either exists or is likely to be discovered. 



Having now placed the reader in the possession of all the facts, 

 we must conclude, not without regret that the present article 

 should, by the very necessities of the case, have taken so contro- 

 versial a tone. Prof. Miiller, however, needs not our praise, and 

 will, we hope, consider our free criticism as a much higher testi- 

 mony to the weight of hi3 authority and the value of his opinions, 

 than any laudation. 



Indeed, as in the instance of his admirable researches upon the 

 Echinoderms, we trust that he will be the first to throw the clear 

 light of observation upon the mysterious obscurity with which 

 this interesting subject is invested, and so restore the zoological 

 world to its propriety, from which his announcement had well 

 nigh frightened it. 



We cannot end better than with two excellent passages, in 

 which some finger-posts are set up for future travellers in this 

 path : — " For the present the solving of this problem is impos- 

 sible, but on the other hand, the kind of work necessary for its 

 solution may be readily pointed out. We do not yet know all 

 that is to be seen in Sijnapta digitata, and there are other kinds 

 of Synapta to be investigated. The spermatozoa of the genera 

 of the Pectinibranchiata, and also in other families of the Gas- 

 teropoda where they are as yet unknown, must be made out. We 

 must learn those of not only one species of Natica, but of all 

 kinds which occur in the Mediterranean and Adriatic seas. We 

 must ascertain the nature of the yelk in Natica, or those species 

 of mollusks to which the nature of the spermatozoa guides us. 



