Introduction to Animal Morphology. 355 



even-edged, hair-margined pleurae over the gills {hranchioste- 

 gites). The post-abdominal pleurae have smooth surfaces 

 gliding on each other ; those of the first and second overlap 

 the preceding segments, while those farther back are over- 

 lapped by the pleurae in front. The brain arises from the 

 early fusion of six ganglia. The second maxilla has a spoon- 

 shaped epipodite {Jlagellum, scaphog7iathile). A few develop 

 with very little metamorphosis, others begin life as Nauplii, 

 consisting of an anterior unsegmented part, with swimming 

 bristles behind (head and swimmeret), and as growth proceeds 

 intermediate parts form, producing a prosoma (thorax), 

 mesosoma (abdomen), and a metasoma (post-abdomen). 

 The following families are included : — i. Palinuridae — Spiny 

 Lobsters ; pereiopods separated medially by a wide sternum ; 

 antennae long (Palinurus), or flat (Scyllarus). The ovum de- 

 velops from its nauplius stage into a Phyllosoma, or com- 

 pressed, transparent pyriform larva, with stalked eyes, a wide 

 cephalothorax, and a small segmented abdomen, with long 

 thin legs. 2. Astacidae — cephalothorax laterally compressed ; 

 post-abdomen flattened ; anterior pereiopods large, chelate ; 

 gills numerous. The larva in Astacus only differs from the 

 adult in the undeveloped tail ; in Homarus in the presence 

 of exopodites on the pereiopods, and the absence of some of 

 the uropods. The freshwater Astacus diff"ers from the marine 

 Homarus anatomically in having fewer gills, longer hepatic 

 caeca, a large undivided caecal remnant of the umbilical 

 vesicle, while Homarus has a smaller, bilobed sac ; but it has 

 a dorsal, single, rectal caecum, which Astacus has not. 

 Homarus has also an undivided telson and a small rostrum. 

 Callianidea has respiratory appendages to the pleiopods. 

 Nephrops is often sold under the name of Prawn. 3. Carididae, 

 Shrimps — shell horny, flexible ; cephalothorax and abdomen 

 laterally compressed ; sternum linear ; gills few ; their larvae 

 have no cephalothorax nor post-abdominal legs ; large 



Siagonopods, while maxillipedes two and three are the first and second 

 Gnathopods. The ambulatory legs are called by him Pereiopods, and the 

 post-abdominal Pleopods ; the hindmost three, when expanded, are 

 called Uropods. 



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