and the Genealogy of the Arthrojjoda. 451 



genealogical tree of the Arthropoda, which must possess a 

 special interest for the readers of this journal. 



Hackel derives the Vermes and Arthropoda from a common 

 root, which stood in genetic connexion with the Infusoria, 

 and from which the Rotatoria have also originated. The Ar- 

 thropoda then divide into two large sections {Cladus) : — the 

 CarideSy CriLStacea (Branchiferous Arthropoda) ; and the Tra- 

 cheatttj Insects (Tracheiferous Arthropoda). Hackel very 

 correctly justifies this division by saying that the orders of 

 Arachnida, Myriopoda, and Insecta are more closely connected 

 than certain families of the Crustacea ; and it seems pretty 

 certain that the Tracheata were only developed from the 

 Carides. Paleontology, indeed, furnishes but little evidence 

 upon this point ; but more is offered by the developmental 

 history of individuals ; and it is well known that the larvae of 

 certain Neuroptera for a long time retain branchial respiration, 

 which they only subsequently exchange for tracheal respira- 

 tion. As, however, it is to be regarded as an established law 

 that the development of an animal in the ts[^^ and in the 

 larval state (the ontogenetic development) is only an abridged 

 and partially obscured picture of the development of a genea- 

 logical tree (the ])hyletic development), we are justified (as 

 also for many other reasons) in di-awing this far-reaching con- 

 clusion as to descent from so remarkable a phenomenon as the 

 change in the mode of respiration in the larvae of Neuroptera. 

 Hence, also, developmental history, the study of which has 

 now been taken up with fresh vigour, acquires an extraor- 

 dinary importance ; and it is to be hoped that the necessary aid 

 will not be denied on the part of entomologists : and this will 

 consist essentially in their undertaking a description and sys- 

 tematization of the larvae as well as the description and clas- 

 sification of the perfectly developed insects, and in ascertaining 

 by observation the external changes which the body of the 

 larva undergoes until it becomes transformed into the perfect 

 insect. 



I will not enter into the details of the develoj)ment and 

 descent of the Crustacea, but only refer to the hypothetical 

 order of the Zoepoda^ which, according to the concordant opi- 

 nions of Fritz Miiller and Hackel, included the progenitors of 

 the Schizopoda {My sis, Euphausia), and consequently of the 

 Stomatopoda, Decapoda, and all the Edriophthalma originating 

 from these, as also of the Tracheata. The assumption of this 

 order is founded upon the Zoea, so well known to all crustaceo- 

 logists, a developmental form in the ontogenesis of most 

 Podophthalma, which refers us back to the Zoepoda. The 

 unknown common original form of the Arachnida, Myrio- 



