274 COMPAEATIVE ANATOMY. 



pairs of lobed glands ; in the Galeodea they are partly represented 

 by coiled tubes, and in the Aranea, likewise, these organs do not 

 appear to be wanting. The salivary glands are highly developed in 

 Mites, where there are several pairs of them, which vary in structure ; 

 the secretion of them is probably partly used as poison. 



In the Myriapoda, there are simple tabular (Julus), or lobed 

 (Lithobius), or even racemose glands (Scolopendra), which are 

 probably salivary. 



In the Insecta the salivary glands are very variously developed 

 as to number, form, and histological structure. It is therefore 

 certain that they also vary greatly in function. It is in a few only, 

 as the Ephemerida, Libellulida, and Aphides, that they appear to be 

 completely wanting', or only feebly developed, as in the Myrmeleonida 

 and Sialida. In others, they are long coiled tubes, or lobed or 

 greatly-branched organs, which frequently accompany the enteric 

 canal for a certain distance. There are often two, and not uu- 

 f requently three pairs of them, which vary greatly in structure. As 

 to their external form and their distribution in the different groups 

 of the Insecta — they have the form of a pair of long tubes in the 

 Coleoptera, Diptera, andLepidoptera; in the order of the Hemiptera 

 and Orthoptera branched, racemose, or lobed forms predominate, 

 as also in many Coleoptera. 



2) Appendages of the Mid-gut. 



§ 213. 



Another group of glandular organs is differentiated from the mid- 

 gut. They are regarded as a liver. According to their points of 

 connection with the enteron, two different organs must be here dis- 

 tinguished from one another. One of them is connected with the 

 most anterior portion, and has the form of simple or branched tubes, 

 which, when more largely developed, form a compound glandular 

 apparatus (cf. § 208). The ends of these tubes seem to be secretoiy 

 organs, but their ducts, owing to their wide lumen, form cavities of 

 the enteron. The organ is, therefore, not yet completely differenti- 

 ated from the enteron. This arrangement is seen in the Branchio- 

 poda, and, among them, most markedly in the Phyllopoda ; some 

 have a simple or branched.caecal tube on either side (Fig. 136, K) ; in 

 others it is converted into a liver (Limnadia, Apus), the greater part 

 of which is placed in the cephalic shield. The Cirripedia have similar 

 organs. In the Arthrostraca these cascal tubes (Fig. 143, A h) are 

 long organs, which pass backwards and vary in number. They are 

 not branched, but this is compensated for by their increased length. 

 They have the same form in the Schizopoda, but in most of the 

 Thoracostraca, as in all the Decapoda, they are formed by a paired 

 mass of glandular matter, which fills up the cephalothorax and is 



