NEUTER INSECTS. 223 



are broken down or reabsorbed, just as in the human embryo the gill- 

 arches disappear, or are transformed into organs required in the next 

 higher stage. 



If, in the insect pupal stage, the development of the higher struct- 

 ural stage begins simultaneously with, or immediately after, that of a 

 lower stage, the latter is interfered with by a superior energy. It can 

 not obtain full unfoldment, and may gain but a rudimentary forma- 

 tion, which may be immediately reabsorbed, to answer the demands of 

 the superior modifying energy. Two unlike energies seem fighting 

 for the nutriment, and the stronger wins. Instances of this principle 

 of development are common in embryo growth, and act to check or to 

 completely abolish the unfoldment of ancestral features. In the case 

 of the ant we may look upon it as the cause of the lack of appearance 

 of the worker characteristics in the development of the queen, and of 

 their full development where the conditions are such as to prevent the 

 innate powers of sexual unfoldment from coming into play, and to 

 restrict development at a lower level. It need scarcely be added that 

 in the case of these insects the check to development is final. On 

 leaving the pupa-case, they enter upon a life of active nutrition, in 

 which the powers of development already in operation may produce 

 their full results, but in which the latent higher powers are definitely 

 restrained. In all cases of insect development, and doubtless to a cer- 

 tain extent in all animals, a state of passivity is requisite to active 

 transformation of tissue, while simple growth is the prevailing tend- 

 ency in states of activity and abundant nutrition. In these latter 

 states organic development may proceed, but it is simply the com- 

 pletion of lines of development which began in the passive state. New 

 lines of development do not begin during nutritive activity. Of this 

 principle many illustrations might be given, had we the space here to 

 adduce them. 



In the case already cited, of the hydroid polyps, this principle of 

 development yields some remarkable results. In many instances the 

 sexual individuals unfold into the full medusoid type, and leave the 

 colony to enjoy a free life. In others they remain attached to the 

 colony, and are more or less checked in their full development. This 

 check to development is so great, in certain instances, that a mere bud 

 appears, to bear the generative products. Thus the sexual, instead of 

 being the typical form, remains as a formless protrusion of the polyp 

 stem, or the germs may originate in this stem with no form develop- 

 ment. 



Yet this seeming anomaly is not without its explanation under the 

 above principle. Where free Medusae are produced, the sexual organs 

 and products do not appear until after full development and freedom 

 from the colony are attained. In the other cases mentioned the gen- 

 erative products appear earlier, and it is probably their appearance 

 that checks further form development. The innate tendency to de- 



