442 CRUSTACEA MALACOSTRACA. 



and many Decapods. It is known as the appendix interna 

 or stylamblis (Fig. 319). In many cases, at least, it carries 

 hooks, and serves, with its fellow, to couple the pair of limbs 

 together. 



The presence of a masticatory stomach has already been 

 alluded to as a feature of the Malacostraca (p. 351). The 

 Stomatopods are remarkable in the disposition of the hepatic 

 glands, consisting of caeca segmentally arranged along ducts 

 which open anteriorly into the stomach (Orlandi). A somewhat 

 similar arrangement is found in the Pagurid Coenobita* 



The position of the genital apertures in relation to the 

 segments is, so far as it has been ascertained, constant 

 and characteristic : that of the oviduct on the sixth, that of 

 the vas deferens on the eighth thoracic segment. In either case 

 the position of the apertures may be on the sternite of the 

 segment, or (some Decapoda) on the coxopodites of the limbs, or 

 on the arthrodial membranes at the bases of the limbs. 



The segmental glands of the second antennae often act as 

 excretory organs in adult Malacostraca, although those of the 

 second maxillary segment replace them in Stomatopods, the 

 Chelifera, some Isopods and the Cumacea. In Nebalia the 

 glands of both segments coexist in the adult. 



The central nervous system of the Leptostraca and of Apseudes 

 (Chelifera) (Fig. 241) approaches very closely to the condition 

 found in the Phyllopoda. The ganglia of the second antennary 

 segment have joined the brain, of which they form the posterior 

 lobes, but a transverse commissure passing between the two 

 longitudinal bands of the oesophageal ring and behind the 

 oesophagus apparently contains the commissural fibres which 

 unite them with one another, and thus by its position records 

 their original postoral situation. Each pair of appendages 

 behind the second antennae is represented by a distinct pair 

 of ganglia, and double longitudinal commissures run throughout 

 the series. In the larva of Nebalia a seventh abdominal ganglion 

 is present (corresponding to the seventh abdominal segment), 

 behind that of the last limb-bearing segment. In some members 

 of the higher groups, as Sphaeroma (Isopoda) and Euphausia 

 (Schizopoda), the nervous system is in an almost equally simple 



* Cf. Borradaile, in Gardiner's Fauna and Geography of the Maldives 

 and Laccadives, Vol. i., p. 80. 



