( oO'J ) 



representative species, one of the descendant forms remains identical with the 

 original form ; bat considering that in all widely distributed groups of representative 

 forms a considerable time must have elapsed before the insects could spread over 

 the whole area — for instance, from North- West India to the Solomon Islands — it 

 is at least in such cases more probable that the form now inhabiting the country 

 where the ancestral form lived has also more or less changed in characters. And 

 this is the more likely to be true as we know from experiments that the time required 

 to bring about a change in colour in Lepidoptn-a is very short, and as we further 

 know that a change, within a short time, has taken place in the famous Porto Santo 

 rabbits, some birds, and a great number of plants. From the comparison of 

 Beasonal forms, which are the more different the greater the contrast of the seasons 

 is, with artificially produced varieties, we can with safety conclude that the 

 degree of divergency of representative forms largely (not entirely) depends 

 on the intensity of the transmuting factors, and that therefore a wider gap 

 between two otherwise allied forms does not necessarily imply that the two animals 

 or plants have been separated for a longer time than less different allies. As 

 it is also well known that the intensity of the biological factors does not gradually 

 increase or decrease as we proceed from one (geographical) extremity of the range 

 of a group of representative forms to the other extremity, it is evident that the 

 degree of diversity of two forms can be independent of the geographical position 

 of the areas inhabited, and that the more similar forms can live widely apart, while 

 the more dissimilar forms may live closer together. 



Though the differences between representative forms are the effect of the 

 action of some kind of local biological factors, it does not follow with necessity that 

 the respective factors are found in every place where a certain form now occurs ; 

 on the contrary, we have instances that species when living under different con- 

 ditions do not show any change in their characters. For example, the island of 

 Kalao, south of Celebes, is inhabited by the Celebensian Papilio rhesus, and the 

 Kalao individuals are to our knowledge not distinguishable from the Celebes rhesus. 

 The other species of Papilio found on Kalao (and Djampea, which is close by) are 

 all conspicuously different from the Celebensian representatives, and have mostly 

 developed to peculiar forms not known (as such) from anywhere else ; hence there 

 must be biological factors peculiar to those islands which have not had any effect 

 on P. rhesus. That rhesus is a true Celebensian insect (i.e. originated from the 

 ancestor of P. aristeus on Celebes) is virtually proved by its characters being (luite 

 analogous to those of many other Celebensian forms. Curiously enough, on the 

 island of Djampea, which lies north of Kalao and therefore is somewhat closer to 

 Celebes, Mr. A. Everett obtained no specimens of rhesus, but a long series of the 

 Malayan representative P. aristeus hermocrates, during the same mouth when 

 he found a good series of individuals of P. rhesus and no hermocrates on Kalao. 

 The fact that rhe.ius is the same on Celebes and Kalao admits three explanations: 

 (1) The biological (trausmntiiig) factors are in respect to rhesus the same on both 

 islands, which would mean that uu Djampea, as iniiabited by a representative, the 

 corresj)onding factors must be different. (2) The biological factors are different on 

 Celebes and Kalao, but the characters acquired by rhesus under the action of the 

 Celebensian factors have become inlieritable. (3) The characters oi rhesus and its 

 representatives are not acquired under the influence of biological factors. 



If, however, a change in the biological factors does not necessarily imply that 

 a change in the characters of every liwng being will take jilace, it is intelligible 



