478 CRUSTACEA MALACOSTRACA. 



its allies. In the latter genus, according to Fritz Miiller, they 

 bear at their bases otocysts, as in Anaspides and the Decapods, 

 though this observation has not been confirmed by later writers. 

 The second antennae bear in Apseudes an oval scale-like 

 exopodite, recalling that of Anaspides and the Stomatopods. 

 The mandibular palp may be present (Apseudes) or absent 

 (Tanais}. The first maxilla bears a backwardly directed setose 

 flagellum at the base of its outer lamella as in Cumacea and the 

 Leptostraca and the Lophogastridae. The second may be small 

 or absent. Attached to the base of the maxillipeds is a stalked, 

 scoop-shaped, membranous appendage which lies in the respiratory 

 chamber, and is evidently homologous with the epipodial plate 

 of the maxilliped in the Isopods and Holotrophous Schizo- 

 pods, and apparently with the posterior plate of this appendage 

 in the Cumacea. It does not appear that this, or any other 

 structure of the Tanaidae is a true branchia, but by its move- 

 ments and that of the flagellum of the first maxilla, water is 

 kept flowing through the respiratory chamber, in the outer 

 wall of which the blood circulates in a large sinus. 



The second thoracic limbs end in powerful chelae, like those of 

 the next pair but one in the Decapods. In Apseudes the third pair 

 is large and fossorial. In this genus also, both second and third 

 pairs bear minute exopodites at their bases (Fig. 294, cf. Cuma- 

 cea). With the exception of the oostegites, mentioned below, 

 epipodites are absent from the seven posterior thoracic limbs. 

 As in Amphipods and the Phreatoicidae among the Isopods 

 the three posterior thoracic legs are directed forward. The 

 five anterior abdominal appendages ('their number may be 

 reduced) are natatory. They resemble one another and consist 

 of two simple flattened setose lobes borne on a basal joint. The 

 sixth are filiform and project beyond the hind end of the body. 

 In these features the Chelifera resemble the Isopods, but the 

 abdominal appendages are not modified as branchiae, as in that 

 order. In accordance with the position of the paired respiratory 

 chamber in the anterior part of the thorax, the heart also is 

 thoracic, and it does not supply arteries direct to the abdominal 

 appendages, as it does in Isopods (Delage). 



A shell gland is present on the second maxilla (Glaus). In 

 some cases sexual differences in the shape of the first two pairs 

 of legs and in other features may be marked. 



