PSYCHE. 



A GENERAL SURVEY OF THE MODES OF DEVELOPMENT IN 

 INSECTS AND THEIR MEANING.* 



The mode of development in all of 

 the first series of orders from 1-1X [see 

 Psyche v. 6, p. 13] is as a rule direct, 

 and this necessarily unites the Thysanu- 

 riform larva, when it is present, .more 

 or less closely with the adult stages, 

 and the adults are apt to show traces of 

 this connection in the retention of cer- 

 tain primitive characteristics. The ab- 

 sence of a waist or deep constriction be- 

 tween the thorax and the abdomen is due 

 to the fact that the junction with the 

 metathorax remains in most adults as it 

 is in the larva and in Thysanura. The 

 mouth parts also are for biting, except 

 in the highly specialized Hemiptera, in 

 which, although the suctorial character- 

 istics of these parts are developed early, 

 the larvae, with this exception, have 

 what may be called a Thysanuriform 

 stage. The highly specialized adults 

 of groups having indirect development 

 (Coccidae) are not exceptions to this 

 rule, and retain to a recognizable de- 

 gree the primitive form of the larvae. 



The second series of orders from X- 

 XVI have, as a rule, more complicated 

 modes of development, introducing va- 

 rious intermediate and often extraordi- 

 nary stages, such as grubs, caterpillars, 



*From Guides for Science Teaching, No. VIII. By 

 Alpheus Hyatt and J. M. Arms. 



etc. Following Brauer and some other 

 entomologists, we have regarded these 

 as more or less degraded modifications 

 of the primitive Thysanuriform larva, 

 but have spoken of them collectively as 

 the secondary larval stages. They ap- 

 pear subsequently to the Thysanuriform 

 stage, when that is present, or between 

 the ovarian and pupal stages when that 

 is absent. The pupal stage is similar 

 to that of the first series of orders in all 

 respects except that, as a rule, it is in- 

 capable of motion, or is what is called 

 quiescent, and is usually more or less 

 protected. The complicated develop- 

 ment of individuals in the second series 

 of orders has led sevei - al authors to des- 

 ignate the first series of orders as Ame- 

 tabola, and the second series as 

 Metabola. 



The use of the term "ametabola," as 

 applied to the orders from I to IX, in- 

 volves an exaggeration, since it implies 

 that they have no metamorphoses ; 

 whereas, as pointed out by Comstock 

 and others, the Coccidae have a "com- 

 plete" series of metamorphoses, or in- 

 direct development, even including a 

 quiescent pupal stage in the develop- 

 ment of the only winged form, the 

 male. The quiescence of the pupal 

 stage loses much significance in view of 



