220 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. 
tudinal and external circular coat; the fibres are all striped. The lining 
epithelium is not much developed, but forms a thick, hard, and very re- 
fringent cuticula that is thrown up into ridges, that may be armed with 
spines. The chitinous lining, or the cuticula, is undoubtedly always 
secreted by an epithelium, 314 and does not belong in the series of con- 
nective tissues, as Leydig has maintained. 315 It will be seen that these 
features are common to all the subdivisions of the anterior segment of the 
digestive canal, the principal variations being in the form and develop- 
ment of the ridges, and the muscular layers, as I have already described 
in detail. The thick cuticula of the " Vordcrdarm" has been observed 
in many insects, 318 and of all orders. 
The second division of the alimentary canal is distinguished from the 
first by the epithelium being composed of very high cylindrical cells, 
which make up the greater part of the thickness of the walls ; by the pres- 
ence of a very delicate, and but slightly refringent, cuticula, and the ab- 
sence of ridges; by the unstriated muscular coats, and, finally, by the 
development of glandular follicles and folds. The ventricle and divert- 
icula have all these peculiarities in common, while no other part of the 
digestive canal resembles them in the least. Essentially the same pe- 
culiarities distinguish the "Mitteldarm" of Phthirius inguinalis. Leach 317 , 
except that there are no glandular follicles. Landois 318 has wrongly ho- 
mologized this part with the crop of the Orthoptera. 
The third division (intestine and rectum) has an epithelium, the cells 
of which are intermediate in size between those of the first and second 
division. The cells are often pigmented; they are covered by a cuticu- 
la much firmer than that of the ventricle, but not so thick and hard as 
that of the first division. The very refringent cuticula is not trans- 
formed into ridges, though in some parts it is covered with delicate 
conical spines, which are very short. The epithelium and underlying 
connective tissue {tunica propria) are thrown up into six folds, which 
run longitudinally, being regular in the ileum and rectum (as the rectal 
glands), but very irregular in the colon. Outside the depression between 
each two neighboring folds there is a longitudinal muscular band, thus 
making six bands. This peculiar disposition of the longitudinal muscles 
does not occur in any other part of the canal ; it is therefore especially 
characteristic of the third division. From this statement of the charac- 
teristics of the three divisions, it is evident that the gastroileal valves 
belong to the third. 
The curious repetition of the number six may be pointed out here. I 
cannot but think it will be ultimately found to have some hitherto un- 
suspected meaning. There are six rows of teeth in the proventriculus, 
311 Semper: Ueber die Entstehung der Schuppen bei den Lepidopteren. Zeit. Wiss. Zool., VLLL Cf. 
also, Gegenbaur, Chun, Braun, et al. 
315 Leydig: Vom Bau des Thierschen Korpers, p. 38, ff. 
316 For example : Phthirius inguinalis Leach. Graber. Z. Z. XX II, 141. 
317 Grafter.- Zeit. Wiss., Zool. XXII, 142-144. 
3l * Landois: Zeit. Wiss. Zool, XIV, p. 1, and XV, 502. 
