426 N. E. McINDOO 



SUMMARY 



In making a comparative study of the disposition of the ol- 

 factory pores in Orthoptera, both sexes of twenty-one species, 

 belonging to twenty genera and representing the six families, 

 have been examined; also, the pores on the first and last instars 

 of the croton-bug (Blattela germanica) and on all six instars of 

 the common grasshopper (Melanoplus femur-rubrum) have been 

 carefully counted. Olfactory pores are more widely distributed 

 in Orthoptera than in any other order yet studied. They were 

 always found on the legs, antennae, and anal stylets; usually on 

 the wings (if present), abdominal segments, cerci, head, and all 

 the mouth-parts, and sometimes on the thoracic segments and 

 ovipositor. Relative to the antennae, olfactory pores are pres- 

 ent on only the first and second segments; occasionally a few lie 

 on the first segment, but always many on the second segment. 

 This is the first time that the writer has seen these organs on the 

 antennae of adult insects, except several on the base of the an- 

 tenna of the honey-bee and a few on the base of the antenna of 

 a certain weevil; nevertheless, they are common to the antennae 

 of all the larvae yet examined. The number of them on the 

 wings is comparatively few, while the mouth-parts are abundantly 

 supplied with pores. 



The total number of pores found on the entire integument 

 varies from 271 to 1616; the mantids and phasmids have the 

 smallest number, certain acridids have the largest number, while 

 most of the remaining species have a medium number. The 

 newly hatched croton-bug has 44.5 per cent as many pores as 

 has the adult female croton-bug; and comparing the total number 

 of pores found on each of the six instars of the grasshopper (Me- 

 lanoplus femur-rubrum), we have the following figures: first in- 

 star 46.3 per cent, second instar 50.5 per cent, third instar 53.2 

 per cent, fourth instar 60.7 per cent, fifth instar 94.2 per cent, 

 adult male 94.3 per cent, and adult female 100 per cent. 



In distribution and external structure, these olfactory pores 

 resemble the lyriform organs of spiders more than do the same 

 organs in any other order yet examined. They are generally ob- 



