vni NEPIDAE NAUCORIDAE BELOSTOMIDAE 565 



of the egg. It will be recollected that we have described (p. 

 562) an egg, apparently of the same nature, deposited by Capsids 

 in the stems of land plants, so that it is very doubtful whether 

 the threads are really connected with the aquatic development 

 of the embryo in Nepidae. But the most interesting feature 

 connected with these eggs is, according to Korschelt, the mode of 

 development of the filaments, which is sui generis ; the shell of 

 the egg is developed in the ordinary manner as an exudation or 

 excretion from epithelial cells ; but the shell of the filament is 

 formed as an intracellular product ; a mode of chitin-formation 

 that appears to be peculiar to this structure. Korschelt remarks 

 that " it is in the highest degree worthy of attention how by 

 any process of development through a large number of successive 

 generations so complex a condition could be established as the 

 result of adaptation to external conditions ; and this becomes 

 even more interesting when we remember that highly peculiar 

 special processes and departures from the usual modes of tissue- 

 formation are necessary to permit the development of this 

 apparatus." l 



Fam. 22. Naucoridae. -No ocelli, and no terminal process 

 to the body ; front legs inserted on or near the front of the 

 prosternum. Anterior femora usually broad and fiat. The 

 members of this family are truly aquatic, and swim readily in 

 the water. The family is small, including about nine genera 

 and thirty species, but, like many water-Insects, the genera are 

 widely distributed. We have two in Britain one of them, 

 Xaucoris, common ; the other, Aphelocheirus, rare. 



Fam. 23. Belostomidae. -<Vb ocelli, and no long terminal 

 tube to the body ; front legs inserted near the front of the pro- 

 sternum. Posterior tibiae not spiny ; flattened and provided with 

 swimming hairs. Although these Insects have been classified 

 with Nepidae they have but little relation therewith ; on the 

 other hand, the distinctions from Naucoridae are far less im- 

 portant. The family includes some of the largest Insects. The 

 South American Belostoma grande attains a length of four or four 

 and a half inches. Notwithstanding their considerable size 

 Belostomidae exist in very large numbers in some localities, and 

 frequently destroy young fish by aid of the powerful though 



1 Korschelt, Ada. t.c. p. 245. Compare the remarks we have made on p. 559 as 

 to the peculiarities of eggs of many other Hemiptera. 



