Introduction to Animal Morphology. 355 



even-edged, hair-margined pleurae over the gills (branchioste- 

 gitcs). The post-abdominal pleune 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 (flagdlum, scaphognaihite}. 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. Astacidoe 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 differs from the marine 

 Homarus anatomically in having fewer gills, longer hepatic 



a, a large undivided caecal remnant of the umbilical 



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

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



marus has also an undivided telson and a small rostrum. 

 Callianidea has respiratory appL'ndagrs to the plrinpiuls. 

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



rimps shell horny, flexible ; cephalothorax and abdomen 

 laterally con. rnura linear; #ills f<-'w ; their lar\;c 



have no cephalothorax nor post-abdominal l\u r s; large 



^onopods, while maxi; the first ami second 



v him /', 1 the 



post 



: L'rvpods. 



\ 2 



