Classification in Zoology. 231 



which, after being cast in the last moulting, are succeeded 

 by the more perfect membranous wing, which in its turn 

 undergoes such a development as to assign to those Lepidop- 

 tera, which have their wings folded backwards and enclosing 

 the body, a position below those in which the wings spread 

 sideways ; and the highest position to those which raise their 

 wings upwards. So that these investigations have settled 

 even the relative position of the secondary minor groups in 

 each of these orders, and though, as yet, imperfectly traced 

 out, they have at least shewn the principle upon which a 

 natural classification of these animals might be carried into 

 the most minute details, without ever leaving any point to 

 arbitrary decision. Similar results have already been arrived 

 at in other classes ; as, for instance, among Medusae, where 

 naked-eyed Discophori, with alternate generations, must be 

 considered as the lowest type, recalling, in one of their con- 

 ditions, the appearance of the inferior class of Polypi ; when 

 the covered-eyed Discophori, with their strobiloid generation, 

 begins in its lowest state with a medusoid polyp. 



Similar facts are known among Echinoderms, in which, 

 among Crinoids, the highest free forms begin with germs pro- 

 vided with a stem, thus assigning, on embryological grounds, 

 a lower position to all those which are provided wi^li a stem. 



In the same manner has it been possible to determine the 

 position of Bryozoa among Mollusca below Ascidise, upon the 

 ground that their embryonic development is similar. It has 

 been possible, in the same way, to assign to Pteropoda a 

 position inferior to that of Gasteropoda proper, and not 

 intermediate between Gasteropoda and Cephalopoda, as 

 anatomical investigations would seem to indicate. For it 

 is now plain that the spreading appendages of the body of 

 Pteropoda are not analogous to the long tentacles which 

 encircle the head in cuttle-fishes, but correspond to the 

 vibratory rudders of the embryo in marine Gasteropoda. 



Again, the position of Foraminiferae seems to me no longer 

 doubtful. They are neither microscopic Cephalopoda nor 

 Polypi, as of late it has been generally thought best to con- 

 sider them, but constitute a truly embryonic type in the great 

 division of Gasteropoda, exemplifying in this natural division, 



