82 THE ENTOMOLOGIST. 



that it is to protect them from numerous enemies, viz., fish, 

 insects, and so forth. He thinks, however, that the hatching 

 time of the young nymphs tends in general towards the end of 

 winter and the middle of spring, and rarely continues after the 

 end of April. It is not so with copulation and oviposition, which 

 take place particularly in winter and spring (and also in summer 

 and autumn). The ova may thus wait many months after 

 oviposition before hatching. As the level of the water is subject 

 to being lowered, they would find themselves liable to exposure 

 to the air and consequent desiccation ; but, as it is, they are 

 concealed in a plant which protects them, and furnishes them 

 with the moisture indispensable to their preservation. Later, 

 the rains of autumn and winter raise the water-level, and the 

 nymphs being again submerged, hatch, and find the conditions 

 necessary to their development. 



The ova hatch in about fifteen days, diving down head fore- 

 most on emerging, and there are four nympbal instars (in part 

 roughly figured by De Geer), the young swimming upside down 

 from the first.* 



Notonecta is subject to water-mites, as are the other aquatic 

 bugs. The odour emitted by the boatman is apparently of a 

 faecal nature, at least no openings similar to those in Ili/ocoris 

 have been found ; it is very similar to that of the plant " stinking 

 goose-foot" {Chenopodiuni vulvarium). 



Notonecta has been found by Enock to be subject to the 

 attacks of a Hymenopterous parasite, viz., Prestivichia aquatica, 

 which oviposits in the ova of the Notonecta. 



There is but a single British species : — 



1. N, GLAucA, Linne. Varies in general colour from pale 

 ochreous to black ; in all the mature British examples I have 

 seen the scutellum is black, but in a North African variety it is 

 yellow. The following varieties are well-marked, though inter- 

 mediate forms occur : — 



(a) glauca, Linne. Tegmina pale ochreous, more or less 

 specked laterally, &c. ; abdomen above black, lateral margins 

 narrowly pale. 



(b) marginata, Thunb. Tegmina black, with two elongate 

 ochreous spots on the clavus, &c. ; abdomen as in the preceding. 



(c) mannorea, Fabr. Tegmina rich yellow-brown, mottled 

 with a darker brown ; abdomen as in the preceding. 



(d) maculata, Fabr. Tegmina orange irrorated with brownish 

 red and blackish brown. Abdomen above orange banded with black. 



A beautiful variety from the Canary Isles (canariensis, Kirk- 

 aldy), which may be a good species, has purple-black tegmina, 

 irrorated with dark rich castaneous. 



■-'= According to Eegimbart, the nymphs of Corixidae present, at their 

 exckision from the egg, no trace of air on their ventral surface ; they are 

 heavier than the water, and appear to commence taking in air only at the 

 end of four or even six days. 



