DEVELOPMENT. 99 



medusa, into which lie supposes it to pass by direct metamorphosis. He refers it to the genus 

 yEf/inoj]sis, Brandt, and names it JEr/inopsh Mediferrcniea, Midi. Miiller docs not seem to liavc 

 obtained any specimen of his j-E. Med'derranca, so far matured as to present traces of the 

 generative elements ; but his observations have been in this respect supplemented by Kollikcr,' 

 who afterwards obtained the same species at Messina in a sexually mature state. 



Now, we cannot overlook the fact that Miiller has not, in the above case, traced his ciliated 

 hydroid through a continuous series of developmental phases into the adult form of jEjinojmH ; 

 and, without denying the probability that the ciliated bitentacular hydroid is really the larva of 

 the JEffinopsis, we cannot regard this relation as absolutely proved, wJiile there is no evidence 

 whatever that the ciliated form is the immediate result of the development of an ovum. Indeed, 

 its remarkable resemblance to the singular generative zooid of Bicoryne (see above, p. 31) 

 would seem to show the probability of another origin than that by direct development from 

 the egg. Midler, led apparently by the analogy of the planula-stage of the Hydroida, considers 

 the ciliated condition of the surface as affording evidence of such a direct development ; but the 

 fact that the Dicori/ne-7jOo\A is also richly ciliated over its whole surface shows that this argument 

 goes for nothing. 



Kolliker" found in the stomach-cavity of a ten-tentacled iEginidan medusa, captured in the 

 sea at Messina, and described by him under the name of Enrydoma rnhiyinosiim, a number of 

 small organisms resembling medusae in various stages of development, and which he believed he 

 could follow from stage to stage until he found them assume the form of a sixteen-tentacled 

 medusa. To this last, which also belongs to the family of the yEyinida, he gives the name of 

 Stenoyaster complanatus. 



The great difference betvveen these two medusae appears to Kollikcr sufficient proof that 

 the one could not have been produced by the other, and he regards the young stenogasters as 

 having been swallowed by the Eurystoma. He views, however, the young Stenoyaster, exhibiting 

 as it does, various steps in a metamorphosis from a very early stage, as affording evidence of the 

 direct development of Stenoyaster from the egg. It is, nevertheless, plain that there are no more 

 valid grounds for such a conclusion in this instance than iu Johan. Miiller's case of j^yinopsis, 

 while Fritz Muller's case of Cunina Kollikeri, as well as the cases described by Gegenbaur and 

 by Keferstein and Ehlers, and the more recent observations of Haeckel, all of which are cited 

 above (p. S3), suggest the probability that the stenogasters noticed by Kolliker originated as buds 

 from the Eurystoma. 



Other instances which have been adduced as affording evidence of direct development from 

 the egg without the intervention of a trophosome have been already referred to as cases where 

 the medusa passes through a series of metamorphoses before arriving at its adult state. They 

 are i\rCrady's case of Cunina octonaria, Fritz Miiller's of Liriope cathariensis, and Haeckel's 

 of Glossocodon euryhia and Carmarina hastata, all of which, from the very imperfect state of 

 development in which the earliest stages of the medusae present themselves, have been regarded 

 by their describers as instances of direct development from the egg, though there is no positive 

 evidence of such an origin ; and, lastly, there is the instance afforded by Trachynema, the ciliated 

 condition of whose youngest di.^covered stage has led Gegenbaur to consider it also as a case of 



^ ' Zeit. fiir wissensch. Zool.,' 1853, vol. iv, p. 327. 

 ' Ibid. 



