488 MISSES K. TOOT AND E. C. STKOBELL 



EXPLANATION OF THE PLATES. 



All the preparations were photographed at exactly the same magnification (20 dia- 

 meters), and the photograph of each intromittent organ was carefully measured with 

 a small pair of architect's dividers, fitted with number nine needle-points, and set at 

 2 mm. The dividers were frequently tested by measuring a line of a definite length. 

 The measurements were made on matte prints, so that each division of 20 mm. could be 

 identified by a pencil-mark and numbered. Measurement of the longer and more closely 

 coiled organs was facilitated by dotting the first coil with red ink, the second coil with blue 

 ink, and leaving the third coil black. In this way tbe longest coil could then be measured 

 with as much accuracy as the shortest. The measurements were made from the distal end 

 of the intromittent organ to the point where the thick part of the coil enters the gland. At 

 this point the coil is easily dissected ofiE (e. </., photos 12 & 13), bat even in those cases 

 where part of the canal within the gland has been preserved {e. g., photo 1) the point from 

 which the measurement was taken is easily determined, for the part within the gland is 

 transparent and quickly tapers to a very fine canal. 



The intromittent organs of photos 1 to 66 are from the same insects which were 

 photographed in an earlier paper and published in this same volume of the Journ. Linn. 

 Soc, Zool. (see Plates 28 to 34). 



In order to demonstrate whether these two exclusively male characters — the genital 

 spot and the intromittent organ — are linked in inheritance, we have placed the intromittent 

 organs of photos 1 to 66 in exactly the same order in which the photographs of the bugs 

 themselves were placed on the plates of the above-mentioned paper — each photograph in the 

 two sets of illustrations exactly corresponding, and thus admitting an accurate comparison 

 of the genital spot and the intromittent organ of each individual bug of the entire series. 



The photographs are reproduced by the half-tone method. Frequently it does not 

 accurately reproduce the distal end of the intromittent organs, which always terminate in a 

 clean-cut oblique angle: this is sometimes obscured by the dotted effect of the half-tone 

 method, giving the appearance of a broken, jagged end. In some cases the reproducers 

 have attempted to correct this by retouching ; but this has not always been successful. 



Plate 41. 

 ( Cf. Plate 28 of this volume.) 



Photo 1. Intromittent organs from the two bugs of photo 1, plate 28. On the left 

 E. variolarius, and on the right E. servus. Length of intromittent orgau of 

 JE. variolarius 95 mm., of .E". servus 167 mm. 



Photo 2. Intromittent organs from the seven E. variolarius of photo 2, plate 28. These 

 insects were raised in our laboratory during the summer of 1912. The parent 

 bugs were raised in our laboi'atory during the summer of 1911, and were 

 kept in captivity during the winter of 1911-12. Lengths of the intromittent 

 oro-ans of the seven bugs are as follows : — 1st (upper), 96 mm. 2nd, 101 mm. 

 3rd, 96 mm. 4th, 93 mm. 5th, 90 mm. 6th, 96 mm. 7th, 92 mm. 



Photo 3. Intromittent organs from the five E. servus of photo 3, plate 28. The bugs 

 were collected in North Carolina in the fall of 1912. Lengths of the intro- 

 mittent organs : — 1st (upper), 1641 mm. 2nd, 164^ mm. 3rd, 175^ mm. 

 4th, 166 mm. 5th, 170 mm. 



Photo 4. Intromittent organ of the wild E. servus of photo 4, plate 28. This male 

 fertilized the E. va?-iolariiis female used for our cross-breeding experiments. 

 Length of intromittent organ, 166 mm. 



