424 EEYIEWS. 



Busch, Ecker, Frantzius and Gegenbaur have since ascertained that 

 a like series of transformations would seem to mark the life-history 

 of the two Bhizostomatous genera, Cephea and Cassiopeia.^ 



Still more extended inquiries have proved that many forms of 

 Corynida? and Sertularidse bud forth free-swimming reproductive 

 bodies closely resembling, in every anatomical feature, not a few of 

 the apparently perfect animals which constitute the division of Cryp- 

 tocarpa?. 



To appreciate such facts aright the student must ever bear in 

 mind the existence of a most perfect and wonderful series of transi- 

 tional structures, connecting those highly differentiated " Zooids" 

 with the simple reproductive processes occurring in a few genera of 

 Hydrozoa ; processes which may truly be said to differ in their con- 

 tents alone from any other portion of the body -wall. 36 As a sup- 

 plement to the preceding remarks it may seem strange to add that 

 the observations just noticed, though highly valuable in themselves, 

 were not needed to demonstrate the necessity for uniting into a single 

 class forms so closely resembling one another in structure as the 

 Discophora and fixed Hydrozoa. An appeal to anatomical evidence, 

 had such been carefully made, ought of itself to have sufficiently shown 

 the desirability of such an arrangement. The study of their develop- 

 ment, however, affords a new and striking proof of the true morpho- 

 logical relations which unite together the organisms in question, 

 while, at the same time, it discloses the existence of a still more inti- 

 mate genetic connection subsisting between them. 



Perhaps no special department of Morphology has of late years 

 brought to light results at once so complete and satisfactory as that 

 which proves the close nature of the relationship between the plant- 

 like Corynidae and SertularidaB on the one hand, and the oceanic 

 Siphonophora on the other ; 37 a relationship which their obvious dis- 



35 Consult, in addition to the English translation of Steenstrup on the Alterna- 

 tion of Generations, Ray Society, 1845, the essay of Gegenbaur — Zur Lehre vom 

 Generationswechsel und der Fortpflanzung bei Medusen und Polypen, 1854, for 

 references to the works of the various authors mentioned in the above paragraph. 



35 On this subject the recently-published memoirs of Allman are of primary im- 

 portance. See his paper — On the Structure of the Reproductive Organs in certain 

 Hydroid Polypes, R. S. E. Proc. 1857-8. Additional Observations on the Morpho- 

 logy of the Reproductive Organs in the Hydroid Polypes, ibid, 1858; and Notes on 

 the Hydroid Zoophytes, A. N. H. 1859-61, passim. 



a7 In the Ann. S. N. for 1841 (torn, xvi.), an excellent memoir on the structure 

 of Stephanomia appeared from the pen of Milne Edwards. For the student of the 

 history of zoology this paper possesses a considerable interest, as being by far the best 

 and most complete account of a Siphonophorous Acaleph which had, up to that time, 

 been published. It was followed by the essays of Mr. Huxley, read before the Royal 

 and Linnean Societies in 1849. In these the true nature of the Siphonophora, and 

 their affinity to the fixed Hydrozoa and Medusidre, received very complete elucida- 

 tion ; yet, OAving to certain delays on the part of the Linnean Society, the views of 

 Mr. Huxley were at first but imperfectly announced and remained comparatively un- 

 known until the year 1851, when the same observer, contemporaneously with Leuck- 

 art, again directed attention to the curious morphological problem which the organi- 



