318 



TEXT-BOOK OF ENTOMOLOGY 



irregular curved and zigzag secondary folds. The cells of the epithe- 

 lium are of uniform size, and the layer is covered by a highly 



ref ringent cuticula without spines ; and, 

 like that in the ileuin, it rests on a layer 

 of connective tissue, beyond which follows 



(1) an internal coat of longitudinal, and 



(2) an external coat of circular striated 

 muscular fibres. (Minot.) 



In butterflies (Pontia brassicce), in Sphinx 

 ligustri, and probably in most Lepidoptera 

 the colon is distinct from the rectum, and is 

 anteriorly developed into a very large more 

 or less pyriforni or bladder-like caecum 

 (Figs. 309, 310), which in certain Coleoptera 

 (Dyticus, Fig. 320, d ; Silpha, Necrophorus, 

 etc.) is of remarkable length and shape ; 

 it also occurs in Nepidae (Fig. 327). In 

 the cockroach a lateral caecum " is occasion- 

 ally, but not constantly, present towards its 

 rectal end," and a constriction divides the 

 colon from the rectum. (Miall and Denny.) 



The rectum The terminal section of 

 the hind-gut varies in length and size, but 

 is usually larger than the colon, and with 

 thick, muscular walls. In Lepidoptera it 

 is narrow and short. 



The rectum is remarkable for contain- 

 ing structures called rectal glands (Fig. 

 298). Chun describes those of Locusta 

 r/ri(h'ssima as six flat folds, formed by a 

 high columnar epithelium and a distinct 

 cuticula; there is a coat of circular bands 

 corresponding to the furrows between the 

 glands. Minot states that this description 



FIG. 319. Digestive" canal of is applicable to the locusts (Acrydiidic) he 

 /.,.;, ,:,,, : ff,_anterior hag inves ti ga ted, the only difference being 



in the structural details of the single 

 layers. He claims that the rectal folds 

 "do not offer the least appearance of 

 glandular structure," neither is their func- 

 tion an absorbent one, as Chun supposed. From their structure and 

 position Fernald regards the rectal glands of Passalus as acting like 



imisrli-s of the pharynx : //, 

 airns ; /, fri/zar<l ; A". cliylr-Monmi-h ; 

 /., ilium ; M, colon (OUTM! part of): 

 A', colon; O, rectum; <i. frontal 

 t:an<,'lion on the vajrus ; //. \airus 

 nerve; c, anterior lateral piiiL'iion 

 connected with th- \airus. A fin- 

 Newport. 



