40 



the Danish physiologist rightly recognized the anatomical 

 structure and contents of the generative organs of the larval 

 Aphis, he might have discerned a much closer relationship 

 between the ovaria and the act of larval propagation than 

 between this and the uterus. 



When, in regard to the analogous generation of the 

 Medusa, Prof. Steenstrup says that the polypiform Scy- 

 phistoma " is a precedent generation of the kind in ques- 

 tion," viz. e alternate generation/ and that the Strobila (e is 

 a precedent individual or preparative individual/ 5 it seems 

 to me that we have here only a different and more formal 

 mode of expressing Siebold's and Sars's facts : viz. that the 

 individual form of the Medusa, which Sir J. G. Dalyell 

 called the Hydra Tuba, precedes the more perfect form, and 

 that the next larval individual, which Sars called ' Strobila, 9 

 is preparatory to the production of the young Medusa. 



It does not explain why the Hydra precedes the Strobila, 

 or how the Strobila prepares the Medusa. The conditions 

 of the organization that render the gemmation of the Hydra 

 Tuba and the spontaneous multifission of the Strobila pos- 

 sible are not pointed out; these phenomena are left as 

 unexplained as they were before : at least the words that 

 " they take place agreeably with the law of alternate gene- 

 ration," and the metaphorical comparison of the Hydra 

 and Strobila with ( wet-nurses } (Ammeri), bring no in- 

 formation as to the organic conditions of the phaenomena : 

 the facts, as discovered by Sars and Siebold, remain just 

 as absolute and empirical as they were before*. 



They have, however, been grouped together with corre- 

 sponding phaenomena in other species, and some of their 

 analogies have been pointed out for the first time by Prof. 



* This the clear-headed Norwegian observer strongly felt when he 

 asked : " Und wie will man denn die Stolonenbildung, die doch deut- 

 lich genugund schon von Siebold an den achtarraigen Medusen-ammen 

 beobachtet worden ist erklaren?" and was compelled to answer: 

 " Davon sch weight Steenstrup." Sars, Fauna Littoralis Norvegica, 

 fol. 1849, p- H. 



