10 William T. M. Forbes 



formed in abnormal surroundings. In the period of change from 

 larva to pupa, specimens have been found to be most sensitive to 

 external conditions, but the effect may be perceptible throughout 

 larval life. 



Thirdly come food-varieties, which are, perhaps, sometimes of the same 

 nature as strains, sometimes as seasonal forms, but associated with 

 differences in larval food. Aside from the minor cases of stunting 

 from unfavorable food, and of exuberant growth with favorable, there 

 is at least one case, that of Halysidota* tessellaris, where definite forms 

 are associated with different food plants. 



Mendelian forms, like races, breed true so long as pure. They do 

 not need to be segregated locally, but act as units in inheritance. Some 

 are dominant, their characteristics appearing in every individual that 

 carries the factor that causes them; others are recessive, only appear- 

 ing in those individuals that happen to inherit the proper factor from 

 both parents. The latter, of course, may be covered up for a series of 

 generations, and then suddenly appear as the result of a favorable 

 mating. The details of this type of inheritance are exceedingly com- 

 plicated, and are explained in several recent textbooks on heredity. 

 Striking cases of inheritance of this type exist in the genus Apantesis. 

 In A. nais it involved the black costal edge, the black-spotted collar, the 

 black face, the red hind wings, and some other characters, each inherited 

 independently of the others. Such Mendelian characters are supposed to 

 have arisen by an abrupt change, or mutation, in the germ of some indi- 

 vidual. Many cases have been studied in the Lepidoptera. Mendelian 

 forms, as well as minor races, are often called strains on account of 

 their tendency to breed true. 



Many variations, lastly, are produced wholly or largely by external 

 causes; and we are ignorant of the true nature of many. These are 

 generally known as varieties ("aberrations" of Staudinger, Jordan, 

 and their followers), or, if rare and widely different from the normal 

 form, as aberrations. 



Monstrosities are deviations in structure from the norm of a species. 

 They may be slight, or so radical as to be incapable of continued life; 

 and may be a result either of an inherited factor, or of some external 

 influence in an early stage. Mere mutilations are not considered mon- 

 strosities. 



It is customary to use as the name of a species its genus and species 

 names. The former is a noun in the singular, and of Latin form; the 

 latter, when an adjective, is made to agree with it in gender. All 

 names of genera are written with a capital, and in entomology it is 

 customary nowadays to write those of all species with a small letter. To 



* This is Hubner's original spelling of the name, justified by its derivation from the Greek. 



