386 u • K. BROOKS ON THE LIFE-HISTORY 



bryos^excepl his opinion that the adult is a Trachomedusa, and must therefore develop 

 directly from the egg, without the intervention of a hydra-stage. 



The Dumber <>f species of Trachomedusae which have been reared from the egg is 

 so small, and these are all so different from Lhnnocodium, that the argumenl from analogy 

 •affords very scanty grounds for rejecting all the published observations, and as a mat- 

 ter of fact, we may well doubt whether Lhnnocodium is a Trachomedusa at albas none of 

 his reasons are conclusive. The younger ones are exactly like medusa-buds, with a closed 

 sub-umbrella, a mouth and a manubrium which have no functional importance, and four 

 radial canals which appear before the opening of the sub-umbrella. In all these respects they 

 agree with medusa-buds and differ from all egg-embryos which have ever been described. 

 There is. therefore, good reason for believing that they are buds, which are detached from 

 a fixed hydra, and this view furnishes an explanation of the fact, so puzzling to Lankester, 

 that among thousands of specimens no females were found. In animals hatched from 

 eggs, wc should certainly expect to find both sexes, and when thousands of embryos oc- 

 cur, ripe females must he present, but a fixed hydroid community gives rise to medusa' 

 of only one sex; and the occurrence in the tank, year after year, of thousands of male 

 medusa', at all stages of growth, without any females, is just what we should expect if 

 they are all the progeny of a single hydroid community, which has been accidentally in- 

 troduced into the tank, and there gives rise to medusa' by budding. The author does 

 not hesitate to resort to hypothetical explanations, and he attempts to explain the ab- 

 sence of females ( 42 ) by the hypothesis that the females may be fixed while the males 

 are free. 



This may prove to be the case, but there is not a single fact in the history of the Ily- 

 dromedusae to give it the least support except his failure to find females and the frag- 

 mentary account of the life-history of Lhnnocodium is therefore an extremely. narrow base 

 upon which to construct the embryology of the Trachomedusa 1 in opposition to the ob- 

 servations of Fol and Metschnikoff. 



Section III. The Anthornedusae. 



Plate 37. 



Turritopsis is a craspedote or veiled medusa belonging to Haeckel's order Antiiome- 

 DUS.E or veiled medusa' without marginal vesicles or otoliths, with ocelli on the bases 

 of the tentacles, with the reproductive organs in the walls of the digestive cavity, and 

 with (inmost cases) four radiating tubes. The Anthomedusae originate, by alternation, 

 from Tubularian Hydroids. 



In the order Anthomedusae, Turritopsis'is a representation of Haeckel's Family Tiar- 

 idje, or Anthomedusae with four broad oral lips, four wide radiating canals, simple on- 

 branched tentacles, four separate reproductive organs in the walls of the stomach, and 

 it belongs to Haeckel's Sub-Family Paxi>.i:ii>.i:, or Tiaridae with eight or more tenta- 

 cles. 



A< a number of allied medusa' were unknown when McCrady's original diagnosis 

 of the genus Turritopsis was published (4S,p. 25) his characteristics of the genus include 



