28 NEOTROPICAL PSELAPHIDAE 



process and courses anteriorly between the intermediate coxae. This fovea is 

 uncommon, but in many Tyrini (certain Hamotus, Neotyrus) is large. 



The following table is given to show the range and distribution of the 

 foveae in a few representative pselaphids. This selected list is made up of 

 Nearctic species, but is applicable to any other faunal area. 



Table I 

 MESO- AND METASTERNAL FOVEAE 



Species I II III IV V VI Total 



Sonoma (Rafonus) tolulae + + + + + f 11 



Rhinoscepsis bistriatus + + + + 8 



Rhexidius canaliculatus + + + + 8 



Bibloplectus ruficeps + f + + 7 



Melba sulcatula + f + + 7 



Euplectus interruptus + + + 6 



Trimiomelba dubia + f + 5 



Rhexius insculptus + + + 6 



Tmesiphorus costalis + f + 5 



Pilopius lacustris + + f 5 



Adranes lecontei + 2 



Legend : + foveae present and paired 



f foveae fused into a single fovea 

 foveae absent 

 See Plate V 



In this table the meso- and metasternal foveal range is from eleven to 

 two. Primitiveness is directly proportional to the number of foveae, if the 

 assumptions set forth here are tenable. Since these eleven species were chosen 

 at random from slides of nearly one hundred species, the confirmation of other 

 lines of evidence is indicative of the phylogenetic value of foveae. Thus the 

 Faronini are the most staphylinoid pselaphids from many points of view, and 

 Sonoma tolulae has eleven out of a possible twelve foveae, whereas the highly 

 specialized Adranes lecontei has but two foveae. In Adranes even the vertexal 

 foveae are lacking; in fact, the dorsal arms of supratentorium do not even 

 reach the epicranium. Sternal foveae also check the relative position of genera 

 within tribes: Rhexidius canaliculatus is more primitive than Rhexius in- 

 sculptus; Melba more primitive than Trimiomelba; Bibloplectus more primitive 

 than Eupleotus. Thus the foveal system should prove phylogenetically sig- 

 nificant when it is more thoroughly studied. 



There is one more structural item which should be mentioned, namely the 

 compound eyes. Rediscovery of Mendelism, followed by the establishment of 

 the gene theory, in the present century has placed at the disposal of biologists 

 a logical mechanism for heredity which can be experimentally attacked (Mor- 

 gan, 1919, 1926). Physiological genetics and cytogenetics have utilized insect 

 material to great advantage within recent years, and the insect eye has played 

 an important role in modern problems. Especially pertinent are the experiments 

 which attempt to explain the facet size and number, their heredity and the 

 role of ecological factors such as temperature (Hersh, 1934; Margolis, 1935; 

 Zeleny, 1915, 1917). Eventually the interrelation between environment and 

 heredity in the insect eye will be sufficiently understood to allow us to evaluate 



