68 DARWINISM chap. 



organs of a species of earthworm (Perionyx excavatus). The 

 normal characters of this sj^ecies are — 



Setfe forming a complete row round each segment. 



Two pairs of spermatheca^, — spherical pouches without 



diverticulse — in segments 8 and 9. 

 Two })airs of testes in segments 1 1 and 1 2. 

 Ovaries, a single pair in segment 13. 

 Oviducts open by a common pore in the middle of 



segment 14. 

 Vasa deferentia open separately in segment 18, each 



furnished at its termination Avith a large prostate 



gland. 



Between two and three hundred specimens were examined, 

 and among them thirteen sjiecimens exhibited the following 

 marked variations : — 



(1) The number of the spermathecge varied from two to 



three or four pairs, their position also varying. 



(2) There were occasionally two pairs of ovaries, each 



with its own oviduct; the external apertures of 

 these varied in position, being upon segments 13 

 and 14, 14 and 15, or 15 and 16. Occasionally 

 when there was only the normal single oviduct 

 pore present it varied in position, once occurring on 

 the 10th, and once on the 11th segment. 



(3) The male generative pores varied in position from 



segments 14 to 20. In one instance there were two 



pairs instead of the normal single pair, and in this 



case each of the four apertures had its own 

 prostate gland. 



Mr. Beddard remarks that all, or nearly all, the above 

 variations are found normaUij in other genera and species. 



AVhen we consider the enormous number of earthworms 

 and the comparatively very small number of individuals ex- 

 amined, we may be sure, not only that such variations as these 

 occur with considerable frequency, but also that still more 

 extraordinary deviations from the normal structure may often 

 exist. 



The next example is taken from Mr. Darwin's unpublished 

 MSS. 



