126 Psyche [October 



less interest than the Annelida themselves [e. g., Dujardina, and 

 other Syllidae) in the study of Arthropodan development. 



The Trilobita and such Crustacea as the Apodidse (together with 

 the Copepoda) are among the most primitive representatives of 

 the Arthopoda, and the Crustacea in particular furnish us with a 

 series of forms from the lowest type to the ancestors of the "My- 

 ropoda" and Insecta, and some of them, such as the Isopoda, 

 Tanaidacea, etc., have paralleled the insectan line of development 

 in the most remarkable fashion, the resemblances in many cases 

 extending even to the minutest details, as I am hoping to show in a 

 series of papers dealing with this subject. The "Myriopoda" ap- 

 parently branched off from the Crustacean stem from ancestors 

 resembling BathyneUa and other Anomostraca, and the Insectan 

 line of development arose near the same point. Some of the lower 

 Apterygota carried over in their development many features in- 

 herited by such " Myriopoda" as the Symphyla and Pauropoda (as 

 is the case with the Protura, Campodeoida, etc.) ; but many more 

 Crustacean features were inherited by the forms leading up to 

 winged insects, such as Machilis, Lepisma, etc., and were carried 

 over in the Ephemerida. 



As is shown in the diagram (Fig. 6), the members of the Palseo- 

 dictyopteroid superorder (i. e., the "Panplectoptera") arose from 

 forms resembling the Panthysanura, or Thysanuroid superorder of 

 Apterygotan insects, and are intermediate between the latter and 

 the Panplecopteroid superorder (with the Panisoptera) . The 

 higher insects {i. e., the Psocoid and Neuropteroid superorders) in 

 turn, arose from ancestors intermediate between the Panisoptera 

 and Panplecoptera, although the "roots" of these stems strike 

 downward into the Paljeodictyopteroid forms also, as is indicated 

 by the carrying over of certain Palseodictyopteroid features in their 

 lines of descent. 



The occurrence of annectent forms intermediate between two or 

 more superorders makes it extremely difficult in some cases, to 

 determine exactly where these forms belong. Thus the Coleoptera 

 might be grouped either with the Neuropteroid insects or with the 

 Plecopteroid iinsects (Dermaptera, etc.), while it is extremely 

 difficult to determine whether to place the Grylloblattoida with the 

 Isopteroid insects, or with the Orthopteroid insects — or even with 

 the Plecopteroid forms. Similarly, the balance of characters in 



