PLANARIA ARETHUSA. Ill 



seasons, conditions, and situations. Scarce 

 has it happened once, when it seems ready 

 to happen again, and still with impunity to 

 the remainder of the animal. Hence the 

 increase of this species advances with in- 

 comparably greater rapidity than that of 

 the other. 



Although it has not been my fortune to 

 find the eggs either of the felina or arethu- 

 sa, those which have chiefly been subjected 

 to observation, I must repeat, that it is 

 not here affirmed there are none. The 

 difficulties opposing the solution of prob- 

 lems far more simple than the secret ope- 

 rations of nature, are a sufficient warning 

 against gratuitous assumptions. Yet in 

 contrasting the various species among 

 themselves, it is certainly very singular 

 that I have never witnessed spontaneous 

 division among those which produced eggs 

 in my possession, or which were disco- 

 vered in the waters. Should this distinc- 

 tion be proved absolute by future observa- 

 tion, it forms an additional phenomenon 



