REVISION OF STREPSIPTERA PIERCE. 175 



which are used in pushing out the cephalo thorax, and perhaps aid in 

 the act of copulation. The necessity of being inconspicuous on the 

 host's body, or rather the necessity of preventing a drying up of the 

 host's interior, has reduced the cephalothorax to a flattened disk 

 which hardly raises the abdominal plates of the host. 



IV. A parasite may by constant reduction of parts become exceed- 

 ingly simple in structure; in other words, generalized. This is, how- 

 ever, generalization by reversion, and is by no means indicative of 

 primitiveness. 



V. Hypermetamorphosis is the extreme of known specialization 

 in development of insects. 



(1) The appearance of the hexapod larva resembling the most 

 primitive of adult insects, followed by successive stages representing 

 various types of larvae, then succeeded by an internally formed pupa, 

 which remains inclosed in its larval skin, and finally the resultant 

 highly specialized male, seems to carry the insect through all of the 

 evolutionary stages experienced in the production of specialized 

 insects. In fact, hypermetamorphosis rehearses the stages of 

 evolution. 



VI. Larviparous reproduction is a modification of biology due to 

 specialization of activities. 



(1) The female strepsipteran never leaves its host, and therefore 

 oviposition is impossible. 



VII. The differing habits of the hosts have given rise to the isola- 

 tion of species of parasites, and their dependence upon a single species 

 of host for nourishment is the result of specialization to meet the 

 requirements of life in that host. 



VIII. A single host may in different localities have different species 

 of parasites in the same genus or group. 



HABITS OF LARV^ OF INSECTS. 



The following generalized table is planned to show the progres- 

 sion of dependence in insect larva?, leading to parasitism. It is, in 

 fact, designed mainly to show that the nature of the parasitism by 

 the Strepsiptera is different from that of any other group of insect. 

 Leading examples only are given. (Acarina are included for com- 

 parative purposes.) 



a. Eggs deposited: 



aa. The egg placed promiscuously 1. 



ab. The egg placed regularly away from larval food 3. 



ac. The egg placed in or on the larval food 4. 



(Tachinida?) Ab. 



b. Eggs not deposited: 



ba. Larvae issuing in presence of food — 



(Sarcophagida?) Ab, Ac. 



(Aphididgp) Aa. 



(Tachinidse) 4b. 



