196 



intestine can be distinctly seen through the last segment]. After 

 death the red tint rapidly fades and then wholly disappears. 

 Tlie iiitersegmenlal membrane forms a double tube or sheath 

 around the tubular tenth segment, and rolls or unrolls on it asa 

 stocking is taicen off. The whole apparatus is everted by blood 

 pressure, and relracted by the muscles. 



Since the ordinary intersegmental muscles (im) in both nymph 

 andadult.are attached to the chitinous ring forming the actual 

 anus, it appears highly probable that this ring represents what 

 remains of an eleventh segment, and accordingly I bave numbe- 

 red it so on the sketcbes, and considered the ectodermal invagina- 

 tioii to be the ordinary intersegmental membrane (imb). It is this 

 part which is giandular on its inner surface, as shown at gl, 

 Fig. 3. 



InLheadult (Figs. 5 atid 6) the same parts are easily dislin- 

 guishaljle, though much modified. Tlie intersegmental membra- 



neous lube and the tenlh tubular seg- 

 ment are considerably shortened and 

 slightly bent, and the segment can 

 now be bat slightly everted, the inter- 

 segmental muscles which retract in 

 into the abdomen having therefore 

 lost theirgreatsize The membraneous 

 invaginated anal portion, however, 

 is even more develoj[)ed Ihan is the 

 nymph, and the retractor muscles are 

 large. 



In the nymph the alimentary canal appears to bave an elastic 

 sheath or membrane over the rectal muscles, from the lower part 

 of the rectum to the end of the canal. Large nervecords from the 

 last abdominal ganglion innervate the relractile segment muscles. 

 Thèse are merely indicated {»c) in the sketcbes. 



In the maie nymph the rudiments 

 of the genitalia are first discernible ^r r ,m 



after the first moult (second instar), 

 al though a slightly depressed or inva- 

 ginated membraneous génital area 

 (ga, a, Fig. 7) at the anterior end of 

 the ninth segment is just visible in 

 the newlyliatched nymph (first instar). Within this ventral area and 

 towards its anterior end, arises at first a very small médian evagina- 

 tion or transverse process(.x, a, Fig. 7); after the second moult (third 

 instar) this becomes differentiated into two ventral anterior evagina- 

 tions or pouches ( g^), and a dorsal posterior médian ponch which is 



