166 



MEKISTIC VARIATION. 



[part I. 



118. Hirudo officinalis : of 7 specimens, 5 had 9 pairs of testes, 



1 had 10 pairs, and though in the 7th specimen there were 



2 pairs, the vas deferens of the last pair of testes ended blindly. 

 Ibid. 



119. Hirudo medicinalis. Fairly often the vas deferens is prolonged beyond the 

 9th testis, and having passed through five annuli, ends in a glandular mass of 

 irregular form. Case given in which the 7 last testes of right side were absent or 

 only represented by amorphous material, the testes of the left side being abnormally 

 large. Ebrakd, Nouv. monogr. cles Sangsues vied., Paris, 1857, p. 99. 



*120. Hirudo officinalis : an individual having a supernumerary 

 penis, and vesicula seminalis of the right side, in the 5th somite. 



vs 2 



vs 



Fig. 26. Case of Hirudo officinalis, No. 120. 



p 1 , penis in normal position ; j> 2 , supernumerary penis ; vs, the usual vesicula? 

 seminales ; vs-, supernumerary vesicula seminalis. (From a diagram sent to me by 

 Mr Gibson.) 



The normal penis in the sixth segment was fully formed and 

 into it opened on either side a vas deferens, provided with a 

 vesicula seminalis as usual. But the vesicula of the right side 

 gave off in addition a vas deferens, which passed forwards into 

 the fourth segment and there enlarged into another vesicula 

 seminalis. This additional vesicula was connected by a duct 

 with a supernumerary penis placed and opening in the middle 

 of the fifth segment. The parts of the left side as well as the 

 female organs were normal. [I have to thank Mr Gibson for 

 furnishing me with a diagram (Fig. 26) supplementing the 

 published account.] Gibson, R. J. Harvey, Nature, 1887, xxxv., 

 p. 392. 



Aulastoma gulo (Horse Leech). In this form as is usual 

 among the Gnathobdellidce there are from 9 to 12 pairs of tes- 



