141 



Morphology of the Abdomen and its terminal parts. 



Almost at the beginning of the period stands the work of 

 Richard Heymons, Grundzüge der Entwickelung und des Körper- 

 baues von Odonaten und Ephemeriden (1896), in which he not 

 only made known many new facts of the embryonic develop- 

 ment of these insects, but also demonstrated the existence of 

 twelve segments in the abdomen of 3'oung Odonate larvœ, a 

 number which up to that time had been observed onl\- in the 

 embryos of insects, and which he considers to be fundamental 

 for the class. His results on the appendages and processes with 

 which the body terminates were expressed in the form of a 

 table which is reproduced here, with some shght modifications. 



Fate of Larval Abdominal Parts after Transformation 



{Odonata). 



+ = present. — = absent or feebly developed. 



Heymons emphasised again the absence of any homology 

 between the " inferior appendages " of male Zygoptera and male 

 Anisoptera, already pointed out by Rameur in 1842 (page 14). 

 He also laid stress on his conclusion that the adult Odonata, 

 other than the male Zygoptera, do not possess cerci, as do the 

 Orthoptera, for cxampl(\ 



