286 



NATURE 



[December 29, 1910 



more remote, but even impossible to reach. As the author 

 points out, such dissimilar hydroids as Syncoryne and 

 Stauridium give rise to similar medusae of the genus 

 Sarsia, and on the other hand the dissimilar medusae 



Fig. I. — Ptrsa incolorata, one of the Trachymedusa. 



Bougainvillia (formerly known as Hippocrene or Margelis) 

 and Nemopsis are produced by gemmation from closely re- 

 lated species of the hydroid genus Bougainvillia. An 

 attempt, therefore, to construct a system under which the 



sent exists. For the present, then, we may agree with the 

 author that the nomenclature of the medusa; and the 

 nomenclature of the hydroids must be, in the majority of 

 cases, kept distinct, but at the same time regret may be 

 expressed that he has not set forth his views of the classifi- 

 cation of these Coelenterates in some tabular form with the 

 families of the hydroids and medusoids arranged in 

 parallel columns. Such a table would necessarily be in- 

 complete and subject to several exceptions in detail, but it 

 would be extremely useful to those who are interested in 

 the Hydromedusa; as a whole and of great assistance to 

 naturalists who are endeavouring to work out their life- 

 histories. Such a table has recently been drawn up by 

 Stechow in a work on the Hydroids of Japan, which was 

 published, unfortunately, too late to be reviewed in 

 Mayer's memoir. A comparison of a table by Mayer, had 

 he constructed one, from the medusoid point of view with 

 that of Stechow from the hydroid point of view, would 

 have given us a very instructive review of the classification 

 of the Hydromedusae as a whole. 



But it seems somewhat ungracious to begin a notice of 

 work that is characterised by so many excellent features 

 by complaining about an omission. 



The first point that will strike the ordinary zoologist, 

 who is not a specialist in any one group, as a very 

 welcome and important novelty in monographs on 

 systematic zoology, is the inclusion in the text of a state- 

 ment concerning all the important contributions to our 

 knowledge of embryology, cytology, and physiology of the 

 subject group. This is not a work that can be set aside 

 as a systematic treatise, of value only when it is required 

 for the identification of a species, but it is one that can 

 and should be consulted by all those who are interested 

 in the morphology of the group. Special attention may be 

 directed to the excellent accounts, given in various places 

 in the text, of the physiology of the rhythmic contractions 

 of the bell, and the lucid statement concerning the recent 

 researches by Stschelkanowzeff on the extraordinary 

 developmental process in Cunina described by Metschnikoff 

 as " sporogony "; but there are many others to relieve the 

 tedium that is inseparable from a series of purely 

 systematic descriptions. 



In dealing with the two genera Ctenaria of Haeckel and 

 Hydroctena of DawydofT, which have been supposed to 

 connect the true Coelenterates with the Ctenophora, the 

 author takes the perfectly sound position that the re- 

 semblances relied upon indicate no true genetic relation- 

 ships between the two classes, but he incidentally directs 

 attention to an interesting observation of Woltereck's that 

 in the larva of Solmundella and in the actinula larva of 



Fig. 2.—Lychnorhiza bartschi, one of the Rhizostome Scyphomedusae. A, Oral view. B, Sense-organ seen from exumbrella side. 



name of the hydroid stage would supersede the name of the 

 medusa stage, or vice versA, even if it were confined to 

 those species of which the life-history is known, would lead 

 to a state of confusion even worse than that which at pre- 



NO. 2148, VOL. 85] 



Tubularia there is an apical pole-plate of ciliated ecto- 

 dermal cells. This does not constitute an aboral sense- 

 organ on such an elaborate scale as that described in 

 Hydroctena, but it indicates, at least, that this organ is 



