42 



ditions of development always showing themselves in a ten- 

 dency to produce abnormalities. 



5. Gonepteryx rhamni. 



(a) Those bred at a higher temperature had a considerable 

 increase in the size of the discoidal spots, and brought to 

 mind specimens which were obtainable in some parts of the 

 Tyrol. 



* (b) Those cooled were females, and had the ground colour 

 considerably more yellow than in the normal forms. This 

 was a form of variation which rarely occurred in Britain, but 

 which had been taken by Mr. Tutt near Bregenz. 



Mr. Tutt remarked that he did not believe that any 

 particular variation was due to any one factor, but to many; 

 although there must be one predominant factor, or more, to 

 cause any particular variation. If altered conditions were 

 imposed for the purpose of iniiuencing development, they must 

 be applied during the histolysis of the pupal structure, at the 

 real time of the formation of the scales. In the consideration 

 of these experiments it must be remembered that the results 

 obtained mainly affected the upper surface ; in the Rhopalo- 

 cera the under sides, which were protective in their coloration, 

 were but slightly influenced. Triphcena orhona and, say, 

 Aglais tirticce were certainly not parallel cases in variation. 

 In the former the upper side was protectively coloured ; in 

 the latter it was the under side. What exposure to cold 

 might do for A . xirtica would not be possible with T. orhona, 

 as only the non-protective surfaces were influenced to any 

 considerable extent by the application of varied tempera- 

 tures. If var. curtisii of the latter species was a remnant of 

 the original form, then the Continental form was a survival 

 of the new. The tendency of the objects of these experi- 

 ments to become darker or lighter was in no way connected 

 with protection. 



Mr. F. Clark exhibited living specimens of parasites of 

 the stickleback {Argulus foliaceus), together with a micro- 

 photograph of the same enlarged thirty diameters. In 

 this the complex structure of the parasite was well shown, 

 particularly the organs for attachment to its "host," these 

 being most perfect in character for that purpose. 



Mr. Tutt read a paper entitled " Is Cold the Cause of 

 Melanism in Scotch Specimens of Triphcena orhona {comes) ? " 

 (printed on page gg). 



In the discussion which ensued, Mr. Barrett said that no 

 doubt cold was a minor factor. On one occasion, at the 

 end of March, when there was not the slightest move in 



