NOTASriS LAOUSTRIS. 401 



what s-shaped passages closed by membranes at tlie 

 inner ends, and containing what appear to be the ex- 

 tremely small, filiform, pseudo-stigmatic organs which 

 follow the shape of the tubes and do not project 

 beyond (Fig. 5). This, however, is really a broken 

 condition of the pseudo-stigmatic organ, which has a 

 short, very thin peduncle projecting some little distance 

 outside the pseudo-stigma, and a shortly-pyriform 

 head ; this peduncle, unlike those of the pseudo- 

 stigmatic organs of all other species in the family 

 which I know, is very brittle and usually breaks off 

 short just outside the pseudo-stigma ; so generally is 

 this the case that when PI. XXXIII was printed I 

 had not ever seen a specimen with its pseudo-stigmatic 

 organs perfect, and was not aware of the existence of 

 the club ; but about Christmas, 1886, I asked Mr. E. 

 Bostock to send me a few specimens for duplicates : he 

 kindly did so, not having examined what he sent fur- 

 ther than to see that they were N. lacustris. On looking 

 at them I was surprised to see the exterior clubs to the 

 pseudo-stigmatic organs, and I have drawn one in a 

 perfect condition in PI. XXX, which had not then gone 

 to press. I think the organs must be looked on as 

 becoming abortive ; possibly the time of year may affect 

 the condition, speciniens obtained from the same pond 

 in May were without the organs. Xo interlamellar 

 hairs usually seen. Tectopedia strongly developed ; 

 forming projecting cups, open above and in front, in 

 the cavities of which the first and second pairs of legs 

 are inserted. Lateral opisthophragmatic processes 

 thin but distinct. Apodemata all joined to the sternum 

 and all converging to the anterior edge of the opening 

 for the genital plates ; the second and third apodemata 

 join before reaching the sternum. 



Legs rather long and thin, the fourth pair being 

 considerably the longest and reaching far back, the 

 whole or the greater part of the tarsus projecting 

 beyond the abdomen. The femora of the first pair are 

 usually set inward, but the two distal joints of all the 



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