230 Miscellaneous. 



one and the same species is particularly striking among the Cteno- 

 phorae. In this order there are not even sexual differences among 

 the individuals, as they are all hermaphrodites. In the Discophorae 

 proper a somewhat greater diversity prevails. In the first place, we 

 notice male and female individuals ; and the difference between the 

 sexes is quite striking in some genera, as, for instance, in Aurelia. 

 Next there occur frequent deviations among them, in the normal 

 number of their parts, — their body consisting frequently of one or two 

 spheromers more than usual, sometimes even of double the normal num- 

 ber, or of a few less. And yet, year after year, the same Discophorae 

 reappear upon our shores, with the same range of differences among 

 their individuals. Among Hydroids polymorphism prevails to a greater 

 or less extent, besides the differences arising from sex. Few species 

 have only one kind of individuals. Mostly the cycle of individual 

 differences embraces two distinct types of individaals, one recalling 

 the peculiarities of common Hydrae, the other those of Medusae ; 

 but even the Hydra type of one and the same species may exhibit 

 more or less diversity, there being frequently two kinds of Hydrae 

 united in one and the same community, and sometimes even a larger 

 number of heterogeneous Hydrae. And this is equally true, though 

 to a less extent, of the Medusa type. Yet among Siphonophorae 

 there are generally at least two kinds of Medusae in one and the 

 same community. But, notwithstanding this polymorphism among 

 the individuals of one and the same community genetically connected 

 together, each successive generation reproduces the same kinds of 

 heterogeneous individuals, and nothing but individuals linked together 

 in the same way. Surely we have here a much greater diversity 

 of individuals, born one from the other, than is exhibited by the 

 most diversified breeds of our domesticated animals ; and yet all 

 these heterogeneous individuals remain true to their species, in one 

 case as in the other, and do not afford the slightest evidence of a 

 transmutation of species. 



Would the supporters of the fanciful theories lately propounded 

 only extend their studies a little beyond the range of domesticated 

 animals, would they investigate the alternate generations of the 

 Acalephs, the extraordinary modes of development of the Helminth, 

 the reproduction of the Salpae, &c, they would soon learn that there 

 are in the world far more astonishing phaenomena, strictly circum- 

 scribed between the natural limits of unvarying species, than the 

 slight differences produced by the intervention of man among do- 

 mesticated animals, and perhaps cease to be so confident as they 

 seem to be that these differences are trustworthy indications of the 

 variability of species. For my own part, I must emphatically declare 

 that I do not know a single fact tending to show that species do vary 

 in any way, while it is true that the individuals of one and the same 

 species are more or less polymorphous. The circumstance that 

 naturalists may find it difficult to trace the natural limits of any one 

 particular species, or the mistakes they may make in their attempts 

 to distinguish them, has nothing whatsoever to do with the question 

 of their origin. 



