422 THE INSECTA. § 338. 



The mouth of the larvae of the Myrmeleonidae, Hemerobidae, and 

 Dytiscidae, is of a very peculiar construction. There is no oral orifice, 

 properly speaking, and the maxillae and mandibles are wholly unfit for 

 mastication, the latter being changed into two curved hooks, hollow and 

 with a narrow fissure at their extremity. These larvae bury these hooks 

 in the insects they have seized, and through the cavity of these organs, which 

 communicates at its base with the oesophagus, suck the blood. <^''*' 



A considerable number of the Insecta take no food during their perfect 

 state, the object of their existence being only to accomplish the act of repro- 

 duction. Their jaws are often very rudimentary and are fit neither for suck- 

 ing nor for masticating.''^* In some cases, indeed, not only are these organs 

 wanting, but the oral orifice is closed as with all inactive pupae. '^"' 



§ 338. 



The Digestive Canal of Insecta and their larvae, is more or less long, 

 sometimes extending from the mouth directly to the anus upon the median 

 line ; sometimes forming in the abdomen loops and convolutions. It is 

 retained in place not by a m«esentery, but by numerous fine tracheae, 

 which envelop its entire extent. It is always wholly invested by a homo- 

 geneous peritoneal envelope under which lies a muscular tunic, composed 

 of longitudinal and circular fibres, which are especially developed about the 

 mouth and anus. Internally, it is lined throughout by an epithelium which 

 is extremely thin at the middle portion of this canal, but very solid and 

 composed of chitine at its two extremities. In the middle portion just 

 mentioned, there is a layer of aggregated cells, evidently of a glandular 

 nature, between the epithelium and the muscular tunic. 



The different parts of this canal in the Insecta may be properly distin- 

 guished in the following manner. The first portion is the Oesophagus, 

 muscular, occupying the three thoracic segments and often dilated at its 

 posterior part into a crop (Ligluvies) and muscular gizzard {Proventriculus). 

 Sometimes there is appended to the oesophagus a sucking stomach consist- 

 ing of a more or less pedunculated, thin-walled vesicle, which is multiplicated 

 on itself when empty. 



The second portion consists of a stomach (Ventriculus), in which the 

 chyle is formed, and which is continuous at the point of insertion of the 

 Malpighian vessels, with the third portion of the digestive canal. This 

 third portion commences by a small and usually short Ileum, which is fol- 

 lowed by a Colon, larger and of variable length. This last often has a 

 Caecum at its anterior extremity and terminates posteriorly in a short mus- 

 cular Rcctu?n.^^^ 



18 See Roesel, Insektenbelust. III. Taf. XVII. proboscis of many Bombycidae and Hepiolidae, aj)- 



XVIII. (Myrmeleon), II. Insect, aquit. classis I. pears equally unfit to receive food. Finally, the two 



Taf. I.-III. I^Dyliscus) ; Ratzeburg, Forstinsekt. small, intercrucial maxillae of tlie males of the 



III. Taf. XVI. (Hemerobius). With the larva of Strepsiptera, are wholly inadequate for the func- 



Dytiscus, the body of the maxillae is wholly abor- tions of masticatory organs. 



tive, but always provided with palpi. With those 20 Movable oral organs and an oral orifice are 



of //em eroi?««, the maxillae are small, deficient in wanting with many Oestridae, and Henopidae, as 



palpi, and jilay in a groove on the concave side of well as with the male Coccidae. 



the mandibles ; finally, with those of Myrmeleon, 1 The functions of these different portions of the 



these organs are wholly enclosed in the cavity of digestive canal do not always correspond to those 



the mandibles. ^ of those parts having the same names with Verte- 



lltThe maxillae are rudimentary and very soft brata. Burmeister (Znr HntaTtiesch. (X. Calandra 



with the Ephemeridae, and Phryganidae, in the p. 9) is certainly correct in saying that the stomach 



last stages of their development. The very short is the chylopoietic jiart, thus combining the fuiic- 



