Articuiata. 29 



which continue apterous. Many of the so-called Aptera 

 ought to be withdrawn from this ill-digested group, in order 

 to be placed in their respective families. With regard to the 

 vermes, it appears to me impossible to separate, as classes, 

 the Annelida, the Turbellariae, and the Helminthes ; too many 

 characters unite them, and the analogy in their embryonic 

 development, as far as it is known, is too striking to author- 

 ise the continuance of these classes. It can no longer be a 

 question, then, henceforth, that we ought to leave the intesti- 

 nal worms in the department of the radiata, any more than 

 that the infusoria, at least by far the greater number, con- 

 nect themselves, in my opinion, with the Crustacea by the 

 totifera. 



The vermes, those of them at least covered with a solid 

 envelope, have left too insignificant traces of their existence 

 in the series of formations, and the fossil insects hitherto dis- 

 covered are in too small numbers, and have not been suffi- 

 ciently studied, to render it possible at present to form a just 

 idea of the part they have acted in the different geological 

 epochs which have preceded the present creation. These 

 classes still await their monographs for the fossil species. 



It is not the same with the Crustacea which are found in 

 pretty considerable numbers in the whole series of forma- 

 tions ; and, if they have not been the subject of such numer- 

 ous researches as the fossils of the greater part of the other 

 classes of the animal kingdom, they are still sufficiently well 

 known to enable us to ascertain the progress of their develop- 

 ment from the most remote geological periods. 



The Trilobites, which are unquestionably the most ancient 

 type of the class Crustacea* have been the object of numerous 

 publications and very varied researches, since M. Al. Brong- 

 niart made it the subject of a special monograph. The works 

 of MM. Dalman, Green, Emmerich, and Burmeister, particu- 

 larly deserve to be mentioned in the first rank among those 

 which have contributed most to extend our knowledge of this 

 curious family, and give us correct ideas of their real rela-^ 

 tions to the other articulated animals. The Trilobites appear 

 under the strangest and most varied forms, from their first 

 occurrence in the most ancient palaeozoic formations. This 



