94 



INVERTEBRATE ZOOLOGY. 



cephalo-thorax, Ai'abic for the abdomen. 

 Cambariis : — 



The followini? is the formula for 



III. Gills. 



Remove the branchiostegite from the side upon which the appendages have 

 not been distiirbed, and examine the delicate pliimose gills. For this, immer- 

 sion in water or weak alcohol will be necessary. There are three classes of 

 gills, named according to their point of attachment. 



(1) Podobranehiae, attached to the basal joints of the legs. 



(2) ArtJirobranchiae, attached to the delicate membrane between the skel- 



etal pieces ; of these there are two sorts, anterior and posterior. 



(3) Pleurobranchiae, attached to the lateral body-wall (Pleuron). 



Grills inay occur on every segment between VI-XIII, and each segment may 

 have four, one podobranchia, two arthrobranchiae (anterior and posterior) and 

 one pleiirobranchia. Thus typically a complete equipment would number 

 •4X8^33. Actually, however, a portion of these fail, the resulting arrange- 



