THE STICK- IXSECT. 



170 



Cnio, the fresli-water uiusse], continue tlieir vigorous move- 

 ment long after the removal of the gills from the animal. 

 In conclusion I may state that the different authors who have 

 investigated the matter refer to the " ciliated border " under 

 various names, such as " striated plate " " ciliated pl:i,te," " plate 

 composed of free-filaments or i-ods," " brush-like border " 

 (Hiirchensaum of Frenzel) ; l)ut all these terms convey to our 

 minds exactly the same idea. 



The hind-gut, including the small intestine (PI. XXVIII. fig 1, 

 Is.) and rectum (fig. 1, R.), is, like the foie-gut, lined with chitin. 

 In the small intestine I distinguish two regions — the anterior one 

 broad, with small internal longitudinal folds, and the posterior 

 narrow, the circumference of which is greatly lessened by the 

 deep infolding of the epithelium, the lumen appearing only as 

 six narrow bays. Just antei'ior to the narrowing a circular band 

 of muscle surrounds the small intestine and by its contraction 

 shuts off the anterior from the posterior region. A curious 

 valvular apparatus (PI. XXX. fig. 9, F.) occurs at the anterior 

 orifice of the rectum in the shape of six muscular pyramidal 

 projections inserted by one of their surfaces in the internal wall 

 of the gut, and with the surface adjacent to the rectum slightly 

 hollowed out. The small intestine can be completely cut oS from 

 the rectum by a muscular band on the external wall, which when 

 it contracts brings the six valves together so that the passage is 

 completely closed. 



The rectum (fig. 1, R.) bears intei-nally six longitudinal thicken- 

 ings of large epithelial cells (PI. XXX:. fig. 8, _E.) which have a 

 glandular function, and between the epithelial cells and the 

 basement membrane (fig. 8, Mb.) there ramifies a system of 

 tracheae, suggesting a rather perfect aei'ation of rectal tissues. 



Musculahire of the Alimetitary Canal. 



As always in insects, the gut is provided with two sets of 

 muscles, longitudinal and circular, which extend along its whole 

 length. But in B. rossii there is a marked deficiency of longi- 

 tudinal muscles in the region of the fore-gut, and their place 

 seems to have been in great measure taken by six broad bands of 

 short oblique fibres which belong morphologically to the circular 

 system (PI. XXVIII. fig. 2, Mo.). On the mid-gut the bands of 

 circular muscles are set wide apart, producing the characteristic 

 furrowed appearance of this region of the intestine. 



The longitudinal muscles present some interesting peculiarities. 

 They extend all along the intestine with the exception of the 

 anterior part, as slender fibres equidistant from each other, and 

 numerous branches are given oflf from the main strands. These 

 branches may anastomose where they run close together, or they 

 may taper off into extremely fine threads. The longitudinal 

 muscles beem to ])lay an important part in connection with the 

 morphological significance of the pyriform organs of the posterior 

 region of the mid-gut. The latter are observed to arise either in 

 close proximity to one, or equidistant from two longitudinal 



1 >) >it 



