IV ALIMENTARY SYSTEM 1 23 



by Vom Eath^ on the apex of the maxillary palp of Locusta 

 mridissima, or a compound organ such as we represent in Fig. 6 8 

 may be located in the interior of the apical portion of the palp. 



The functions of the various structures that have been 

 detected are, as already remarked, very difficult to discover. 

 Yom Eath thinks the cones he describes on the antennae and palpi 

 are organs of smell, while he assigns to those on the maxillae, 

 lower lip, epipharynx, and hypopharynx the role of taste organs, 

 but admits he cannot draw any absolute line of distinction 

 between the two forms. The opinions of Kraepelin, Hauser, and 

 Will, as well as those of various earlier writers, are considered in 

 Sir John Lubbock's book on this subject.^ 



Alimentary and Nutritive System. 



The alimentary canal occupies the median longitudinal axis 

 of the body, being situated below the dorsal vessel, and above the 

 ventral nervous chain ; it extends from the mouth to the opposite 

 extremity of the body. It varies greatly in the different 

 kinds of Insects, but in all its forms it is recognised as con- 

 sisting essentially of three divisions : anterior, middle, and pos- 

 terior. The first and last of these divisions are considered to be 

 of quite different morphological nature from the middle part, 

 or true stomach, and to be, as it were, invaginations of the 

 extremities of a closed bag ; it is ascertained that in the embryo 

 these invaginations have really blind extremities (see Fig. 82, 

 p. 151), and only subsequently become connected with the middle 

 part of the canal. There are even some larvae of Insects in which 

 the posterior portion of the canal is not opened till near the close 

 of the larval life ; this is the case with many Hymenoptera, and 

 it is probable, though not as frequently stated certain, that the 

 occlusion marks the point of junction of the proctodaeum with 

 the stomach. The anterior and posterior parts of the canal are 

 formed by the ectoderm of the embryo, and in embryological and 

 morphological language are called respectively the stomodaeum 

 and proctodaeum ; the true stomach is formed from the endoderm, 



^ Zeitschr. wiss. Zool. xlvi. 1888, pi. xxxi. 



- On the Senses, Instincts, and Intelligence of Aninmls, with special reference to 

 Insects. Vol. LXV. International Scientific Series, 1888. 



