2i8 THE POPULAR SCIENCE MONTHLY. 



consideration as to many others, or his remarkable power of analysis 

 could not have failed to perceive other important bearings of the sub- 

 ject. A full review of the phenomena of larval development certainly 

 seems to remove the mystery of the neuter ant and bee from the posi- 

 tion of an anomaly to that of an ordinary method of structural unfold- 

 ment. If the appearance of sexual organs and powers is the final step 

 to maturity, then all neuters are larval forms, although in every other 

 respect their development may be complete ; and they are subject to 

 the same modifying influences as are all larvae. It is one of the most 

 common conditions of invertebrate life-development for the imfolding 

 offspring to stop at certain stages of growth, and devote itself for a 

 while to nutrition, ere resuming its course of structural development. 

 Such " resting-stages " are those in which there exist specially favor- 

 able conditions of nutrition, or of adaptation of the larval form to the 

 conditions of the food-supply. The most notable instances are those 

 seen in the extraordinary larval forms of some of the Echinodermata, 

 and the little less remarkable larval structure of some of the insects 

 and crustaceans. In certain cases several successive larval forms, each 

 deviating considerably from the normal type of the animal, appear. 



Yet these peculiarities of structure have never yet been advanced 

 as stumbling-blocks in the way of natural selection. The caterpillar, 

 for instance, while resembling the moth or butterfly in its more deep- 

 lying peculiarities, displays remarkable external deviations, and as- 

 sumes organs and instincts still more anomalous than those shown by 

 neuter ants. The larval star-fish presents an instance of still stranger 

 anomaly. Only the stomachal region and its immediate surroundings 

 pertain to the type, and all the rest of the structure is accessory. 

 When the development of the star-fish is resumed the new form grows 

 out of this internal region of the body of the bipinnaria, or larval 

 form, whose external parts are discarded as useless, or absorbed as 

 food by the new creature. This is the most aberrant instance of such 

 temporary development known. No trace of the star-fish type can be 

 perceived in its larva. It doubtless exists, but is quite masked by sec- 

 ondary formations. Or it may be that this larva represents an ances- 

 tral form of the star-fish, as divergent in character as is the crustacean 

 larva of the barnacle from the mature form. 



Yet this explanation of atavism, or temi:)orary check to develop- 

 ment at an ancestral form stage, only partly meets the difficulties of 

 the case. There is an unquestionable new adaptation to new circum- 

 stances to be explained. Natural selection acts upon all forms which 

 give it sufiicient opportunity, without regard to whether they are larval 

 or mature. Let us take for an instance the case of the butterfly. Here 

 the development does not proceed continuously, from the germ to the 

 mature form, as in some insects, but is checked for a considerable pe- 

 riod at the caterpillar stage. The active nutrition at this stage seems 

 to act as a check upon development, so that the caterpillar is a form 



