OF THE HYDROMEDUS^. 369 



On the whole Haeckel's error was a fortunate one for science, for it led him to make 

 a very thorough comparative study of the adult Geryonid and Cunina, and this com- 

 parison resulted in his two valuable and beautifully illustrated papers (30), and showed 

 conclusively that the Cuninas are veiled medusa?, not very different in structure from 

 the Geryon'nke, through which they are related to the ordinary Hydromedusse. The 

 Cuninas and their allies had previously been regarded as Aeraspeda, but Haeckel's re- 

 sults, which are now almost universally accepted, form a valuable addition to positive 

 science, although they were based upon this strange hypothesis. 



The next paper in historical order contains no new observations, and is simply an 

 attempt by Allrain (6) to bring Haeckel's hypothesis into harmony with our knowledge 

 of other hydroids. He accepts without question Haeckel's opinion that a Geryonid may 

 give rise to Cuninas by budding, and he sees nothing remarkable in such an occurrence. 

 On p. 469, he says " While the observations of Haeckel, however, can scarcely be too 

 highly estimated for the light they throw upon the relation between tbe Geryonidae and 

 ^Eginidse, it appears to me that he greatly overrates the difference between the genetic 

 phenomena which are here presented and those already well known among the Hy- 

 droida." lie then gives a series of diagrams by the aid of which he attempts to show 

 that the production of medusas by budding from the wall of the stomach of a me- 

 dusa of a totally distinct order, which also reproduces itself normally by eggs, is no 

 more than the analogy of Hydractinia would lead us to expect. He makes no reference 

 to McCrady's paper, with which he does not seem to be acquainted. It is rather strange 

 to find that while he accepts without question the statement that a Geryonid may pro- 

 duce Cuninas by budding, he is half disposed to believe that the Cunina buds found in 

 Cuninas by Gegenbaur, Keferstein and Fritz Midler, are to be regarded as "suggesting 

 parasitism rather than gemmation" (p. 474). 



Metschnikoff's papers (30 «, b, and c), which come next in historical order (1874), 

 are, with the exception of McCrady's papers, the most important ones which have ap- 

 peared, for he gives for the first time a complete life-history of two Cuninas, ^Egineta 

 (Solmoneta) Jlavescens, and ^-Eginopsis (Solmundella) mediterranea. lie proves, by 

 rearing these medusae from the egg, the correctness of the prophecy Johannes Muller 

 made twenty-five years before, that, in these two species at least, there is no alternation 

 of generations, no sessile hydra-stage, and no asexual multiplication. In a third paper 

 (30 a), he shows, as Fol had done a few months before, that Qeryonia ( Garmarina) 

 hastata also develops directly from the egg without alternation or budding. In a third 

 paper (30 c), he gives an illustrated account of the development of the Cunina larvas 

 which are found in the stomach of Cunina, and although he calls attention to the close 

 similarity between the youngest of these larva. 1 and those which he reared from the eggs 

 of JEgineta and .iEginopsis, and although the youngest larvae were found swimming 

 in the stomach, not fastened to its walls, he regards them as buds from the wall of the 

 stomach. His account shows that the history of the larva is very much like that of 

 the one which McCrady studied; that the larva is a hydra; that it multiplies by budding 

 from an aboral stolon, and that the hydra-larva' which are thus produced change into 

 medusae by metamorphosis. He does not refer to McCrady, but it seems strange that 

 he was not led to question the origin of the larvae by budding from the stomach, by 



