36 ANTS. 



complete absence of glands and the presence of a chitinous lining 

 which is continuous at the mouth with the chitinous investment of the 

 body and appendages. The true or individual stomach (ventriculus) 

 which succeeds the proventriculus, represents a sudden departure in 

 structure and function (Figs. 13 and 15, st). It is a small, elliptical 

 sac, hardly capable of dilatation, with very glandular walls devoid of 

 a chitinous lining. This region alone arises from the inner germ-layer 

 of the embryo, in which it is called the mesenteron. Its structure 

 shows very clearly that it is adapted to digesting and absorbing the 

 liquid food that may be permitted to pass the valve at the posterior end 

 of the proventriculus. Though of relatively large size in the embryo 

 and larva, the stomach in the adult ant forms but a small portion of the 

 alimentary tract. The portion lying between the stomach, and anus, 

 and comprising the small intestine (Fig. 15, //;/). Malpighian vessels 

 ( ;;//> ) and the rectum (re), arises in the embryo like the stomodaeum 

 from a tubular infolding of the ectoderm, the proctodseum, and, like 

 the stomodaeum, has a chitinous lining, which in this case is continuous 

 with the integument at the anus and ends abruptly at the junction with 

 the posterior end of the stomach. 



The small intestine is a narrow tube usually more or less wrinkled 

 by the action of its transverse musculature. Its histological structure 

 is similar to that of the cylindrical section of the proventriculus. Near 

 its insertion into the stomach, where it forms a valve, it receives the 

 Malpighian, or urinary, vessels, which are merely so many long, tubular 

 evaginations of its walls. These vessels seem to vary considerably in 

 number in different ants. Thus, according to Adlerz ( 1886) there are 

 6 in Leptothorax, Formicoxenus and Harpagoxenus, 8 in Ancrgatcs, 

 8-10 in Lasins, 12 in Tapinoma, 14 in Polycrgns and 20 in Formica and 

 Camponotus. According to Meinert (1860) the number may vary in 

 the different castes of the same species. Thus the female of Lasins 

 flai'its is said to have 7-14, the male 6-16 and the worker 7-8. Accord- 

 ing to Janet there are 6 in all three phases of Myniiica rnbra. 



The rectum consists of an ampulliform enlargement which narrows 

 posteriorly to its termination in the anus. Its thin walls are furnished 

 with a single dorsal and a pair of lateral lentiform glands. The fasces 

 and the urinary excretions from the Malpighian vessels accumulate in 

 the rectal ampulla and are expelled by a contraction of the thin muscle- 

 layer in its walls. The anus (Fig. 15. an ) is provided with a sphincter 

 muscle and is situated on a papilla, which, in a state of repose, is con- 

 cealed within the small, telescoped terminal segments of the gaster. In 

 the Camponotinre the anal orifice is fringed with a regular row of deli- 

 cate hairs, or cilia. 



