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 



refringent cuticula without spines; and, 

 like that in the ileum, 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 bmssicce), 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 pyriform 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 

 viridissima 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 

 5. 319. <restive canal of is applicable to the locusts (Acrydiidae) he 



has investigated, the only difference being 



single 



Fro 



I. iic, i mix 



iniiM'le> nf the pharynx; //, irsoph- 

 aifii* ; /, fji/./.ar.l ; A", ch\ Ir-i-lcunarli ; 

 7,, ilium ; M, colon u-ieeal part of) ; 

 JV, colon; O, rectum; <i, frontal 

 frantrlion on the vajrns; //, vajrus 

 nerve ; <, anterior lateral ganglion 

 cnniiectecl with the vajJUS. After 



Newport. 



in the structural details of the 

 layers. He claims that the rectal folds 

 "do not offer the least appearance of 

 glandular structiire," 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 



