TV WEISMANN'S CRITICISMS 221 



of parasites, affects in a marked degree some sexual 

 characters, males being made thus to resemble more 

 or less females in external secondary character?, while 

 complete sterility may be induced through action on 

 the essential sexual parts. 



Fertility may thus be affected in many manners, by 

 want of space (Semper), by nutrition (Maupas), etc., 

 and many facts also go to show that external influ- 

 ences have a good deal to do with the nature of 

 segmentation and even with the occurrence of par- 

 thenogenesis. 



As concerns physiological characters, we are also 

 able to induce much modification, by changes in 

 pressure for instance, or by altered food, etc. Through 

 gradual increase of heat we may, as Dallinger has done, 

 accustom certain Monads to live at temperatures which 

 are deadly to them in other circumstances ; Chauveau 

 has shown us how we can profoundly alter the physio- 

 logical characters of micro-organisms, etc. 



At least it seems to us that this conclusion fairly 

 follows from the foregoing facts. But we cannot 

 proceed without saying a word of Weismann's posi- 

 tion in regard to these facts. In one of his essays, 

 On the Supposed Botanical Proofs of the Transmis- 

 sion of Acquired Characters, written a few years ago, 

 Weismann has discussed some cases which are similar 

 to some of those I have related. One of these cases, 



