PROCTOTRYPIDAE 



537 



very peculiar kind of metamorphosis this Cyclops-like larva 

 changes into an almost unsegmented, oviform larva, destitute of 

 appendages ; by a second change this creature assumes a third 

 condition, in which it is similar to the ordinary form of para- 

 sitic Hymenopterous larvae. Sometimes several of the Platy- 

 gaster larvae are found in a single host, but only one of them 

 reaches this third stage. Afterwards the third larval instrar 

 passes into the pupal stage, which lasts five or six days, and 

 then the perfect Insect appears. It is worthy of remark that 

 the internal organs undergo quite as remarkable a change as the 

 outer form does. The metamorphoses of some other Proctotry- 

 pidae have been examined by Ganin, and appear to be of an 

 equally interesting character. 1 



There is reason to suppose that these Platygaster parasites 

 are of great economic importance as well as of scientific interest, 

 for Platygaster herrickii is one of the enemies of the larva of the 

 destructive Hessian fly, Cecidomyia destructor. 



The Proctotrypidae are no doubt extremely numerous in species, 

 but as yet they have been very little studied ; a good work on 

 the British species is much required. A valuable contribution 

 has recently been made to the study of the family by Ashmead, 

 in the book we have already referred to. This volume includes 

 much information on 

 the natural history of 

 these Insects, and the 

 outline figures give 

 some idea of the great 

 variety of external 

 form. 



Many entomologists 

 include the Mymarides 

 in Proctotrypidae, but 

 Ashmead considers 

 that they should be 

 treated as a separate 

 family. Alaptus excisus 

 Westw. (Fig. 354) 

 has been frequently said to be the smallest known Insect, the 



1 See also Kulagin, Zool. Anz. xiii. 1890, p. 418 ; xv. 1892, p. 85 ; and Congr. 

 internal. Zool. ii. 1892, pt. i. p. 258. 



Fia. 354. Alaptus excisus, Westwood. Britain. 

 (Probable size about \ millim.) 



