538 HYMENOPTERA 



measurement given for it by Westwood l being a length of -^ of a 

 millimetre about T ^ of an inch. Mr. Enock has recently 

 examined Westwood's type in the Museum at Oxford, and from 

 his information we may conclude that this Insect is probably 

 the same as Alaptus fusculus Hal., and that the measurement 

 mentioned by Westwood is erroneous, the Insect being really 

 about half a millimetre long. The Mymarides are, however, 

 very minute, some of them not exceeding one-third of a milli- 

 metre in length. Whether any of them are smaller than the 

 beetles of the family Trichopterygidae, some of which are only 

 one-fourth of a millimetre long, may be doubted. 



The Mymarides are recognisable by their very minute size, 

 and by their peculiar wings. These are slender, destitute of 

 nervures, fringed with long, delicate hairs, and stalked at the 

 base. Probably Mymarides may all prove to be dwellers in eggs 

 of other Insects. The group is remarkable from the fact that it 

 contains some of the very few Hymenoptera with aquatic habits. 

 Two species were discovered in their winged condition in the 

 water of a pond near London by Sir John Lubbock 2 ; one of 

 them Polynema natans Lubbock probably, according to Mr. 

 Enock, the same as Caraphractus cinctus Hal., uses its wings 

 freely for swimming under water, while the other Prestwichia 

 aquatica performs this operation by the aid of its legs. This 

 latter Insect seems to be very anomalous, and its position quite 

 doubtful. The embryogeny of Polynema is very peculiar, and 

 takes place in the egg of a dragon-fly Calepteryx mrgo under 

 water. According to Ganin, 3 in the earliest stages the develop- 

 ments of the embryos of the Calepteryx and of the Polynema 

 progress simultaneously, but that of the dragon-fly does not pro- 

 ceed beyond the formation of the ventral plate. The Polynema 

 appears to leave its own egg at an extremely early stage of the 

 embryonic development. It would appear, in fact, that there is 

 no definite distinction between embryonic and larval stages. 

 The information given by Ganin leads to the conclusion that a 

 complete study of this remarkable mode of development is 

 necessary before forming any general ideas as to the nature of 

 Insect embryogeny and metamorphosis. 



1 Tr. Linn. Soc. (2) Zool. i. 1878, p. 587. 

 2 Tr. Linn. Soc. xxiv. 1863, p. 135. 3 Zeitschr. wiss. Zool. xix. 1869, p. 417. 



