236 



KATHARINE FOOT AND E. C. STROBELL. 



DESCRIPTION OF PLATE I. 



The length of the intromittent organs was measured by a small pair of architect's 

 dividers fitted with No. 9 needle points, and the dividers were frequently 

 tested by measuring a 100 mm. line. Each intromittent organ was photo- 

 graphed at a magnification of 20 diameters, and the measuring was simplified 

 by numbering each division of 20 mm. by a pencil mark. The measurements 

 were taken from the distal end of the intromittent organ at the point where the 

 coil enters the gland, the coil being easily dissected off at this point (photos 3, 4, etc.). 



In photos i, 2, 7, 9, a small part of the gland itself is retained. When part of the 

 intromittent organ that is within the gland is preserved, the point from which the 

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

 transparent and tapers at this point to a much smaller canal, e. g., photos 15 and 19. 



PHOTOS i to 4. Typical specimens of the intromittent organ of Eiiscliistus 

 variolarius. Length of the organ of photo i, 98-5 mm. Photo 2, length 97 5 mm. 

 Photo 3, length 95 mm. Photo 4, length 94 mm. 



PHOTOS 5 to 8. Typical specimens of the intromittent organ of E. scrvus. 

 Length of the organ of photo 5, 182 mm. Photo 6, length 158 mm. Photo 7, 

 length 170 mm. Photo 8, length 162 mm. 



PHOTOS 9 to 12. The intromittent organs from four of the Fi hybrids. Length 

 of the organ of photo 9, 124 mm. Photo 10, length 132 mm. Photo u, length 

 122 mm. Photo 12, length 126 mm. 



PHOTOS 13 to 20. The intromittent organs from eight of the Ft generation. 

 Length of the organ of photo 13, 85 -5 mm. Photo 14, length 97 mm. Photo 15, 

 length 140 mm. Photo 16, length 128 mm. Photo 17, length 147 mm. Photo 18, 

 length 100 mm. Photo 19, length 124 mm. Photo 20, length 124 mm. 



