THE CANADIAN ENTOMOLOGIST 285 



THE PROBABLE ANCESTORS OF INSECTS AND 



MYRIOPODS.* 



BY G. C. CRAMPTON, PH.D., AMHERST, MASS. 



In view of the fact that such Crustacea as Bathynella, Apseudes, 

 etc., so obviously fulfil the conditions one would naturally look 

 for in those forms which are supposed to have departed as little 

 as any from the ancestral condition of insects, it is indeed sur- 

 prising that they have been passed over in silence (although they 

 have been known to science for many years) despite all of the 

 speculation concerning the nature of the ancestors of insects, and 

 the various forms which have been put forward as the probable 

 ancestral types. A comparative morphological study of the forms 

 in question, however, has convinced me that they represent quite 

 closely some of the types from which insects have sprung, and I 

 would, therefore, maintain that the Anomostraca (e. g. Anaspides, 

 Koonunga, Bathynella, etc.) and the Isopoda-Amphipoda group 

 (e. g. Apseudes, Ligia, Gammarus, etc.) contain certain forms very 

 like some of the ancestors of both insects and "myriopods" {sensu 

 lato) . 



It should be clearly understood that neither the first insects, 

 nor their immediate ancestors, were of any one single type; but 

 from the very first, the ancestral insects differed greatly among 

 themselves — although the degree of variation may not have been 

 as great as that between the different representatives of present- 

 day Apterygota. Some of the ancestral insects were doubtless 

 quite like the Protura, while others may have borne a stronger 

 resemblance to the campodeoid or other types of apterygotan 

 insects; but the Procura have departed as little as any known 

 insects from the primitive condition of the hexapodan group as a 

 whole, although they have not retained certain primitive features 

 preserved in other representatives of the apterygotan group. 



The developmental tendencies which were to result in the pro- 

 duction of a proturan type of insect with long slender body, com- 

 posed of approximately twenty-one segments (allowing six for the 

 head region, three for the thorax and twelve for the abdomen), 



*CDntribution from the Entomological Laboratory of the Massachusetts 

 Agricultural College, Amherst, Mass. 

 >ugust, 1918 



