220 THE POPULAR SCIENCE MONTHLY. 



the ancestral line to meet certain special requirements of the situation. 

 It can never return to that line. The mere fact that an ancestor once 

 existed, with certain characteristics, has in itself no controlling force 

 upon the development of the embryo. 



The secondary adaptations of larval forms have the same bearing 

 upon development as have peculiar ancestral conditions. They be- 

 come characteristic steps in the line of development to maturity. The 

 sexually mature animal has passed through them all in its growth 

 from the germ, and conditions of the same character are implanted in 

 its own germs, and must unfold in their development. There is no 

 longer an exact phylogcnctic line. Many of the ancestral stages have 

 become greatly modified. To the new developing animals those modi- 

 fied stages of growth are ancestral stages so far as it individually is 

 concerned. Development follows this new line, although it may have 

 become a strangely warped and irregular one, and though at certain 

 stages of growth it may yield peculiar organs or tissues which are dis- 

 carded as useless, or consumed as nutriment, at later stages. The true 

 line of growth in such cases is restricted to the more deep-lying and 

 important parts of the organism, and though, at certain stages of 

 growth, forces appear which produce a special growth of secondary 

 tissue, this is reabsorbed or discarded when the development is re- 

 sumed. Marked instances of such discarded tissue are seen in the 

 pupal development of certain insects, and in the case of the star-fish 

 development above referred to. 



We have paid some little attention to the characteristics of larval 

 growth for two reasons. Their true bearing on the mystery of evolu- 

 tion has been little attended to, and the above-given hypothesis of 

 explanation has not heretofore been offered, so far as the writer is 

 aware. The second reason is that they bear a much closer relation to 

 the phenomenon of neuter insects than might at first sight appear. 

 The neuter insect has not as yet been looked upon as a resting-stage 

 in the line of full development, and as analogous to the lower stages 

 of larval growth. It has, indeed, a peculiarity of its own, that it fails 

 to attain full development. And as its secondary characteristics are 

 not participated in by the sexually mature form, but have arisen by 

 adaptation which is still operative, the fact of their transmission be- 

 comes difiicult to understand. Yet we think it may be shown to be 

 but an extension of the principle above considered. 



It is a significant fact that a neuter worker class is found only in 

 those animal tribes in which the social principle has reached its high- 

 est development, such as the bees, ants, and termites among insects, 

 and the hydroid polyps in the other sub-kingdoms of life. In each of 

 these communal types of life there has been a division of duties, the 

 work of reproduction being confined to one or a few members of the 

 community, at least so far as maternity is concerned, while the other 

 members have gained special adaptations to other duties. In bee com- 



