1897. ARE THE ARTHROPODA A NATURAL GROUP? loi 



a larval form, secondarily arisen, into the organisation of which many 

 later acquired characters have been inserted so as to alter it in various 

 ways. 



To apply this view to the explanation of the nauplius was a 

 natural consequence. A few years later I myself came to this con- 

 clusion, having been caught and held fast by the alluring teaching of 

 F. Miiller, which Haeckel had also enthusiastically taken up ; but 

 when Hatschek had drawn, from an unbiassed study of the develop- 

 ment of the annelids, his conclusion that the nauplius represented a 

 changed trochophore larva, I also tried to point out in my paper 

 " Neue Beitrage Zur Morphologic dei Crustaceen " [Arheiten der Zool. 

 Inst. Wien, 1886), that the nauplius must be looked upon as an 

 altered larval form of the annelid stock with accelerated arthropod 

 characters. " If we cannot distinguish the genetic relations between 

 arthropods and annelids in respect of metamerism of the body, of 

 the similar processes of separation of the segments at the hinder 

 section of the body of a growing animal, and of the general agree- 

 ment in internal structure, especially that of the brain and ganglion 

 chain, of the segmental organs (Peripatus), shell glands, antennary 

 glands, limbs and parapodia, then we have to imagine as the 

 ancestral form of the Protostraca (Archiphyllopoda) an organism like 

 a many-limbed annelid with incipient arthropod characters, especially 

 in the structure of the extremities " {I.e. pp. 93, 94). 



If we view the nauplius form from such a standpoint, the 

 dilemma which Hutton insists upon with regard to the origin of the 

 Onychophora falls to the ground, and there is no reason to disallow 

 the probabilit}' of all classes of Arthropoda having descended from 

 annelids. No one can deny that the Onychophora represent the class 

 nearest related to the annelids. They will therefore correspond to a 

 branch which became cut off from the common stem quite early, 

 even before any important reduction in the segmental organs took 

 place, and acquired in connection with a land-habitat their peculiar 

 tracheal respiration, differing from that of the insects and myriopods. 

 From this stem the ancestral form of the hypothetical Protostraca or 

 Archiphyllopoda may also have arisen. In fact, we have to think of 

 it as having had some such form as I tried to construct at that time 

 ('* Crust. Syst.," I.e. p. 100). Arnold Lang, in his excellent text-book 

 of Comparative Anatomy (1891), has drawn a more complete picture 

 of this supposed stem-form, which corresponds to advances in know- 

 ledge since the time at which I wrote. I can express myself as 

 agreeing in all essential points with this scheme, as regards both the 

 internal structure and external form. 



That the Myriopoda and Insecta which are nearly related to one 

 another, and therefore are sometimes put together in one arthropod 

 class, as Antennata, have the same origin as the Onychophora, 

 appears to me as little admissible as the erroneous view which derives 

 them from an aquatic zoea. More rightly should the Antennata be 



