184 HANDBOOK OF INVERTEBRATE ZOOLOGY. 



a. On its dorsal surface notice the eight pairs of lami- 

 nated, pyramidal gills. The first pair are small and hori- 

 zontal, while all the others are vertical. The first and 

 second pairs are attached to the bases of the second max- 

 illipeds. The third pair lie over the bases of the third 

 maxillipeds, and the remaining five pairs lie above the 

 bases of the five pairs of pereiopods. Notice that each 

 gill consists of a series of plates or leaflets, connected by 

 an external tube, the vessel which carries venous blood to 

 the gills, and an internal tube, the vessel which carries the 

 aerated blood away from the gills. Remove the gills, and 

 clean out the muscles which fill the dee}), honeycomb-like 

 cells of the sternal plastron. 



b. This is now seen to be a complicated hollow box, 

 divided, by great numbers of partitions, into irregular 

 cells. It is made up of the sternal, episternal, and epim- 

 eral portions of the somites which carry the appendages 

 between the first pair of maxillipeds and the last pair of 

 pereiopods. 



1. The united sterna form the smooth, external surface. 



2. The outer or ventral ends of the episfci-nti are visible 

 externally, wedged in between the outer ends of the 

 sterna. They are continued upwards towards the dorsal 

 surface as thin plates between the muscle chambers of 

 adjacent somites. 



3. The united epimera form the sloping dorsal surface. 

 tbeflancs, upon which the gills rest, and they also send 

 plates down to complete the partitions between the muscle 

 cells. 



4. Make sketches of the ventral and lateral aspects of 

 the sternal plastron. 



VI. Clean the carapace, and, on the inner surface of the 

 anterior edge notice the attachment of the eyes, ant en- 



