S. A. Arendsen Hein 



255 



Gradual transitions from one extreme to another, the usual fluctuating 

 modifications, render the classification difficult. Still it appears from the 

 experiments that some of these variations conform to a definite type, 

 so that they can hardly be taken as extreme variants of one series if in 

 the progeny of such a type these extremes return in very large numbers. 

 It is not the place here to enter upon any details of this sort of quanti- 

 tative variation. In this paper I shall confine myself only to the 

 description of rare deviations of a qualitative nature which (although 

 they modify the shape of the prothorax) do not affect the bilaterally 

 symmetrical condition of this structure. 



Fig. 11 c* shows the shape of the prothorax as it is found generally. 

 It is seen that the distal edge displays two small notches right and left. 



r**^ ^-^N 





Fig. 11. 



No. 10. Sometimes this distal edge is anteriorly scalloped in the 

 median line as shown in Fig. 11 c®. 



No. 11. It may also occur that the reverse presents itself, and the 

 posterior edge, in the median line, has grown into an isosceles triangle, 

 the vertex of which is directed distally. Fig. 11 cl 



No. 12. Something like this may also occur in the anterior edge, 

 which, in normal cases, is slightly concave, but it also may appear as a 

 crooked line, the two arms of which, like the two sides of a triangle, 

 converge medially. 



No. 13. Occasionally an abnormal cupola-shaped arching both of the 

 dorsal and of the ventral plane of the prothorax was found. 



