56 Evolution and Adaptation 



the point ; but the issue thus raised is too unimportant to 

 merit further discussion. Leaving aside also some even more 

 doubtful criticisms which are made by Fleischmann, and 

 which might be added to indefinitely without doing more 

 than showing the credulity of some of the more ardent 

 followers of the transmutation theory, or else the uncertainty 

 of some of the special applications of the theory, let us pass 

 to Fleischmann's criticism of the problem of development. 1 



With fine scorn Fleischmann points to the crudity of the 

 ideas of Oken and of Haeckel in regard to the embryology 

 (or the ontogeny) repeating the ancestral history (or the 

 phylogeny). We may consider briefly (since we devote the 

 next chapter almost entirely to the same topic) the excep- 

 tions to this supposed recapitulation, which Fleischmann has 

 brought together. The young of beetles, flies, and butter- 

 flies creep out of the egg as small wormlike forms of appar- 

 ently simple organization. They have a long body, composed 

 of a series of rings ; the head is small and lacks the feelers, 

 and often the faceted eyes. The wings are absent, and the 

 legs are short. At first sight the larva appears to resemble a 

 worm, and this led Oken to conclude that the insects appear 

 first in the form of their ancestors, the segmented worms. If 

 we examine the structure of the larva more carefully, we shall 

 find that there are a great many differences between it and 

 the segmented worms ; and that even the youngest larva is 

 indeed a typical insect. The tracheae, so characteristic of the 

 group of insects, are present, the structure of the digestive 

 tract with its Malpighian tubes, the form of the heart, the 

 structure of the head, as well as the blastema of the repro- 

 ductive organs, show in the youngest larva the type of the 

 insects. In other words the body of the caterpillar is formed 

 on exactly the same fundamental plan as that of the butterfly. 



1 The long argument of Fleischmann in regard to the origin of the fresh- 

 water snails, as illustrated by the planorbis series, and also the origin of the 

 nautiloid group, has been recently dealt with fully by Plate, and, therefore, need 

 not be considered here. 



