DESCRIPTIONS OF GENERA AND SPECIES 



629 



with Kynotus in having a spermiducal gland. Tykonus agrees with Kynotus in the 

 fact that the setae do not commence until about the seventeenth segment, and in 

 the presence of a 'bursa.' On the other hand, the Old -World genus, Microchaeta, is 

 unique among the Old- World genera in having lateral nephridiopores. This genus 

 is regarded by ROSA as being intermediate between his two subfamilies. 



Among the Acanthodrilidae and other earthworms, the number and position of the 

 contractile hearts are of systematic importance ; the position of these varies also in 

 the Geoscolicidae. As a rule the last pair are placed more anteriorly than is the 

 case with the Acanthodrilidae or the Perichaetidae ; in the genus Ilyogenia, for 

 example, the last pair of these commissural vessels are in the eleventh segment. 

 Unfortunately, the blood-vessels have not been studied in a considerable number of 

 Geoscolicidae ; we know, however, the position of the hearts in the following genera : 

 The last pair of hearts in the genus Pontoscolex is in segment xii. 



51 

 V 



Onychochaeta 



Ilyogenia 



Trichochaeta 



Diachaeta 



Urobenus 



Rhinodrilus 



Tykonus 



Anteus 



Geoscolex 



Microchaeta 



Kynotus 



Hormogaster 



Callidrilus 



Siphonogaster 



XI. 



xi. 



xi. 



xi. 



xiii. 



xii. 



xii. 



xii. 



xii. 



xi. 



xi. 



xi. 



xii. 



xii. 



