1 70 DESCRIPTIONS OF PREPARATIONS. 



basipodite. It is slender, and has a long basal joint and a many-jointed filament. 

 The second maxilliped has a smaller and softer endopodite, and a larger exopodite. 

 There is a podobranch but no coxopoditic setae. The basipodite is distinct, and the 

 meropodite very long. The first maxilliped has- the coxopodite and basipodite 

 imperfectly separate and expanded into thin setose plates. The endopodite is short 

 and two-jointed ; the exopodite large, with a much elongated basal joint. The 

 podobranch is reduced to the stem and lamina, and is known as the flagellum or 

 epipodite of Milne-Edwards. The three pairs of maxillipeds belong to the thorax. 



The second maxilla has a very thin lamellate coxopodite and basipodite, each 

 partially subdivided by a fissure. The endopodite is small and simple. The exopo- 

 dite forms a large plate, the scaphognathite, which is kept in perpetual motion 

 and bales the water out of the branchial chamber, into which it runs posteriorly 

 and inferiorly. For its homology see Claus, Untersuchungen zur Erforschung 

 der genealogischen Grundlage des Crustaceen-sy stems, Wien, 1876, p. 42. The 

 first maxilla has two thin simple and foliaceous expansions. The first represents 

 the coxopodite; the second is usually termed basipodite, but the homology is 

 doubtful. The endopodite is extremely reduced, and the exopodite absent. It is 

 present in Euphausia and in the Zoaea of Penaeus up to a certain stage, and then 

 atrophies. 



The sides of the mouth are formed by a soft lip. In front it is overhung by 

 a leaf-like projection, the labrum, attached basally to the epistoma or broad trian- 

 gular calcified area in front of the mouth and extending forwards to the base of 

 the antennae. The sides of the mouth are overhung by the bases of the mandibles, 

 and behind the latter are two small soft lobes united by the posterior margin of 

 the mouth. These lobes are the paragnatha, metastoma, or lower lip. Neither 

 labrum nor metastoma represent appendages in development, but it is possible that 

 the latter represents a dissociated portion of the first maxilla (Claus, p. 15, Neue 

 Beitrage, &c., infra). The ventral region between the bases of the mouth parts, 

 and again between the bases of the first and second antennae becomes calcified, 

 forming a series of sterna. The antennary sternum constitutes the epistoma. 



The rostrum in Nebalia is a moveable process. In Squilla it is jointed to the 

 fore-edge of the carapace and moves with the somite of the first antenna. In 

 Nebalia it appears to belong rather to the region of the first than to that of the second 

 antenna, to which Professor Huxley allocates it. 



The ventral and basal lateral parts of the sternal wall of the mouth-parts and 

 thorax give origin to a number of internal cuticular folds or apodemata. These 

 apodemata constitute the endophragmal skeleton and give attachment to muscles 

 as well as protection to the thoracic portion of the nerve-chain and the sternal blood- 

 sinus. Their arrangement is too complicated to be explained without the aid of 

 figures, and the student may consult Professor Huxley on the Crayfish, p. 157, 

 where will be found both description and figures. 



There remain for examination the two first pairs of abdominal appendages in 

 the male and the telson. 



The first appendage is unjointed and cylindrical. Its apex forms a plate slightly 

 bifid. The sides of the plate are rolled upon themselves, the anterior half surround- 

 ing the posterior, giving rise to a canal open at each end. It is not certain what 

 parts of the typical limb are represented in this appendage. 



