Carpenter, The fossil Isopod (Oxyuropoda) of the Irish Devonian. 667 



In two papers 1 ) on the question of Arthropod relationship 

 I have been able to confirm Hansen's discovery of the 

 maxillulae in the Symphyla (Scolopendrellidea) and to demon- 

 strate the existence of these interesting little appendages in that 

 primitive diplopod Polyxenus. The various groups of arthropods 

 known generally as „Myriapoda" are thus brought into asso- 

 ciation with the Crustacea and Insecta. In particular I have 

 striven to show that Scolopendrella and Polyxenus agree exactly 

 in the numerical segmentation of the body with an isopod, a 

 thysanuran, and a primitive arachnid. Thus all the Arthro- 

 podan classes must be derived from ancestors with a definite 

 number; of Segments, and the development of a large number 

 of somites in such forms as Julus, Geophilus and Apus must be 

 regarded as a secondary condition. 



If the opinion of Lankester and B ö r n e r , that the 

 primitive insects have a special affinity with the Isopoda, be 

 accepted, the discovery of Oxyuropoda is of particular zoological 

 interest. In my own view, a more general relationship between 

 Insects and Crustaceans seems probable, so that Oxyuropoda 

 and the Palaeodictyoptera must be regarded as far along lines 

 of specialisation from their common ancestors. The difficulty in 

 accepting the direct origin of insects from arthrostracans lies 

 in the vastly different specialization of thorax and abdomen in 

 the two groups ; we must surely go back to arthropods with undif- 

 ferentiated trunk-segments before we can reach the common stock 

 of crustaceans and insects. Yet these unknown, primitive crea- 

 tures must have been, on the whole, crustacean in structure and 

 the crustacean characters which we find today in the Thysanura, 

 Collembola and Ephemerida are without doubt inherited survi- 

 vals, indicating a true relationship between the two classes, even 

 though that relationship be remote. 



Diskussion: 



Herr Kustos A. Handlirsch (Wien) bedauert, wegen der 

 Kürze der Zeit nicht näher auf die vom Vortragenden erwähnten 

 Beziehungen zwischen Insekten und Isopoden eingehen zu können. 

 Er habe selbst immer an einer Ableitung der Insekten von bran- 

 chiaten Vorfahren festgehalten und freue sich, diesbezüglich mit 

 Herrn Prof. Carpenter in Übereinstimmung zu sein, doch 

 scheine es ihm, als seien die Isopoden doch schon zu hoch spe- 

 zialisiert, um als Ausgangspunkt für die Insektenreihe betrachtet 

 zu werden. 



x ) Proc. R. Irish Acad. XXIV. (B.) 1903. Qua* . Journ. Micr. Sei. XLIX.1905. 



