202 THE ENTOMOLOGIST. 



Mr. Sturt considers that ventilation is important. The top of 

 the flame of the lamp D should be about two and quarter inches 

 from the bottom of the plate, for which purpose the height of 

 the tripod stand should be regulated accordingly. Night lights 

 may be used in the place of the lamp, but require more frequent 

 attention. 



In preparing the apparatus for use the sunken part of the 

 soup-plate should be packed to the rim as tightly as possible 

 with thoroughly damped moss ; into this twigs, as shown in the 

 figure, should be fixed, up which the insects, as they emerge, can 

 crawl in order to expand their wings ; the pupae should then be 

 arranged on the damp moss, and lightly covered with a thin 

 layer of damp moss ; they soon make hollows for themselves on 

 the surface of the moss, and not unfrequently "kick off the 

 blankets," seeming to prefer to lie bare. The metal compartment 

 beneath the plate should now be filled through the opening F 

 with water at about 100° F., the lamp lighted, and the whole 

 placed away from all draught, which might extinguish the flame. 



The temperature should be maintained between 90° and 110° 

 F., but dampness should not be excessive, for Mr. S. believes 

 that this is one of the chief causes of crippling ; and he therefore 

 contents himself with pouring only a few teaspoonfuls of water 

 round the rim of the plate when he observes the moss becoming 

 dry at the edges. The time occupied by the process of forcing 

 is, in the case of S. convolvidi, from eighteen to twenty days. 

 Insects should, of course, not be removed from the twigs until 

 their wings are fully expanded. 



The great use of forcing comes into pla}^ with the thin- 

 skinned hawk-moths, and it is very interesting to watch the 

 successive changes which take place in them. It does not 

 answer well for the more pachydermatous pupae, and often has 

 disastrous effects upon such as are enclosed in tough cocoons. 



H. Guard Knaggs. 

 London, June, 1896. 



NEW EXPEEIMENTS ON THE SEASONAL DIMORPHISM 



OF LEPIDOPTERA. 



By Dk. August Weismann. 



(Translated from the German by W. E. Nicholson, F.E.S.) 



(Continued from p. 185.) 



A closer observation shows that, even with natural climatic 

 varieties, it is not everywhere wholly a question of the direct 

 influence of the colour-chemistry. The southern var. ichnusa 

 of Vanessd urticce always has less black above in so far as spots 

 5 and 6 are lost, spot 4 is at least smaller, and so is the black of 



