March 1S91.J 



PSYCHE. 



43 



direct modes of development do not 

 show to any marked extent acceleration 

 in the inheritance of adult or adolescent 

 (pupal) characters, but, on the contrary, 

 the characteristics of these later stages re- 

 main remarkably constant in the ages 

 at which they are inherited. They do 

 not encroach upon or replace the larval 

 stage to any very marked extent, as in 

 the examples cited above, among the 

 Orthoptera or Hemiptera. This might 

 be considered as fatal to the application 

 of the law of acceleration, and this 

 would be the case if that law were any- 

 thing more than the expression for a 

 general result of causes which underlie 

 the action of heredity. One of these 

 causes is what we have already expressed 

 as a law of replacement. 



Two modifications cannot occupy the 

 same space, and the secondary larval 

 forms having become fixed in the organ- 

 ization, they hold their own in the de- 

 velopment of individuals against the en- 

 croachment of the pupal and adult 

 characters by virtue of their suitability 

 and the conservative power of heredity. 

 The few cases in which acceleration of 

 the pupal stages at the expense of the 

 larval stages does take place in the sec- 

 ond series of orders seem to show this, 

 since they occur not in the normal forms 

 having the ordinary habitat, but in par- 

 asites like the Pupipara. 



Teachers who read Sir John Lub- 

 bock's interesting chapter on the Nature 

 of metamorphoses will find opposite 

 views expressed in regard to the rank 

 of metamorphoses, and these may con- 

 fuse them unless explained. He speaks, 



on page 41, of the maggots of flies as 

 belonging "to a lower grade" of meta- 

 morphoses than the grubs which have 

 biting mouth parts and heads, and of 

 the caterpillar as on a higher level than 

 the vermiform larvae of Diptera and 

 Hymenoptera. This, literally trans- 

 lated, means that larvae, like those of 

 the grubs of most Coleoptera and Lep- 

 idoptera, have heads, mouth parts, and 

 legs which have not yet suffered from 

 reduction ; but in speaking of these as 

 "lower grade," Lubbock makes a mis- 

 take in systematic perspective. If, as 

 he holds, the secondary larvae are all 

 primarily the outcome of the Thysanu- 

 ran form, they are all what he ought to 

 call "higher grade," being more spe- 

 cialized and farther removed from this 

 primitive insect standard than the larvae 

 of the more generalized or first series of 

 orders. The same and, we think, more 

 philosophical mode of dealing with the 

 facts leads to the corollary that among 

 themselves the larvae of the more spe- 

 cialized orders are really "higher," if 

 the use of this word is considered essen- 

 tial, or more specialized in proportion 

 to the extent of their structural devia- 

 tion from the Thysanuran standard. 

 Thus the larvae of Diptera are, as a 

 rule, more specialized than any other, 

 and have to be set on the extreme left 

 in our table on this account. The words 

 "higher and lower grade" are extremely 

 confusing, since they embrace three dif- 

 ferent classes of ideas, — anatomical and 

 physiological facts and teleological no- 

 tions. Nature leads us along lines of 

 modification which sometimes rise 



