 THE CANADIAN ENTOMOLOGIST 29 



THE NER\'OUS SYSTEM OF THE LAR\A OF STHENOPIS THULE 



STRECKER. 



BY J. M. SWAINE, 

 Entomological Branch, Ottawa. 



(Continued from p. 283, \'ol. LH.) 

 Comparative Studies of the Larval Nervous System in Lepidoptera. 



A Summary. 



A comparison of the nervous system of the larvee of the Jugatse with that 

 of other caterpillars of the Lepidoptera and Trichoptera reveals several in- 

 teresting conditions, two of which appear to have special significance. 



It is not proposed to generalize too freely from the results of these few 

 dissections, but rather to suggest that the well defined differences in the larval 

 nervous system may be worth more exhaustive treatment in connection with 

 the study of the phylogeny of the group. It may be that the larval nervous 

 system in the Lepidoptera and Trichoptera has been less modified throughout 

 the evolution of the groups than has any other organ of either larva or adult, 

 and since the characters exhibited are so distinct that in some cases genera 

 and even species may be determined from them, the evidence they present 

 must be of value. Dissections of determined larvae throughout the Trichoptera 

 and in the lepidopterous families Nepticulidae and Prodoxidse, examples of which 

 were not available to me at the time, should prove of special interest. 



The Lepidoptera were divided by Professor Comstock into two sub-orders, 

 the Frenat?e and the Jugataj, the latter comprising the two families Hepialidae 

 and Micropterygidse. Judged by the characters of the adult the members of 

 the Jugata2 were considered to be the most primitive of the Lepidoptera; and 

 the study of the pupal wing-venation of Sthenopis thule by Dr. MacGillivray 

 supports this view. The most recent catalogues of the North American Lepi- 

 doptera do not recognize this subdivision into Frenatse and Jugata; but place 

 the families Hepialidae and Micropterygida^ as the lowest of the order. Still 

 more recently the Micropterygidse have been included with the Trichoptera. 



It is, therefore, of considerable interest to find that the larval nervous 

 system of Sthenopis and of one species of the Micropterygidae are closely similar 

 in the two most prominent characters and are far more widely separated from 

 all the Frenatae, as represented in our dissections, than are any two families of 

 these so-called higher Lepidoptera, from each other; that in one respect at least 

 they are much more highly modified; and, further, that the larval nervous 

 system of the Trichoptera agrees most closely in these characters with the 

 higher families of the Frenatae. 



The larval stages of the primitive stock from which both Lepidoptera and 

 Trichoptera have descended must surely have had a nervous system of a primi- 

 tive type, and from this the nervous systems of our modern caterpillars and 

 caddice-fly larvae must have been derived. 



Since the nervous system of primitive insects apparently included a double 

 chain of ganglia, longitudinal connectives and transverse commissures through- 

 out the length of the thorax and abdomen, with at least one pair of ganglia in 

 each abdominal segment, evidence of advanced modification should be indicated 



February. 1921 



