448 N. E. MCINDOO. 



of a wing. When one or two groups are present, they He on the 

 radius. When three groups are present, all three may lie on the 

 radius, or two may lie on the radius and the third on the media. 

 When four groups are present, one lies on the subcosta, two on 

 the radius and one on the media. The largest group on the 

 radius usually extends nearly all the way to the fold of the wing 

 and sometimes all the distance to the fold. The number of 

 pores on a pair of wings varies from 130 to 982, 



There are usually two groups of pores at the proximal end of 

 each trochanter. Sometimes a pore is found at the proximal 

 endi'of the femur. It is common to find a few pores at the prox- 

 imal end of each- tibia; and sometimes pores are found in the 

 tibial spines and on the tarsi. The number of pores on all six 

 legs varies from 49 to 341. 



In regard to water beetles, the better the legs are adapted for 

 locomotion in water, the fewer pores they have. The smallest 

 winged species (Coxelus) examined has 273 pores, which is the 

 smallest number of all the species, and the largest species {Ortho- 

 soma) has i ,268 pores which is the largest number of all the species 

 examined. The apterous species have more pores on the legs 

 than usual. As a rule, the smaller the species, the fewer its pores 

 and the larger they are, comparatively speaking. As a rule, 

 there are no generic and specific differences, except variations in 

 number of pores, the amount of variation depending on the sizes 

 of the individuals compared. There are no individual and sexual 

 differences other than slight variations in number of pores. 



The pore apertures or pits are round, oblong, slitlike or club- 

 shaped. On the elytra and wings they are always round or 

 oblong. On the legs they have all four of the enumerated shapes. 



The spindle-shaped sense cells of most beetles lie in the lumens 

 of the appendages outside the pore cavities, but in the legs of 

 Orthosoma the sense cells lie inside the pore cavities. A small 

 chitinous cone is always present. It is formed by the hypodermal 

 cell at the mouth of the pore after the insect has emerged from 

 the last pupal stage, and at the same time when the chitinous 

 integument is being considerably thickened. The sense cells 

 are fully developed when the insect emerges into the imago stage. 

 The sense fiber pierces the cone and the layer of chitin between 



I 



