3 6 CRUSTACEA, 



Turning to the second pair of jaw-feet (d 2), the four 



sections arc quickly recognized ; in the first pair (d i) the 

 fourth section does not bear a "ill. 



The scholars have now found six gills fastened to 

 six of the thoracic appendages, and they may also 

 observe twelve others attached to the consolidated 

 thoracic rings, making eighteen gills on each side. 

 When the animal is walking or feeding, the gills at- 

 tached to the legs are kept in motion. In this way a 

 greater extent of surface is brought in contact with 

 the water, and the aeration of the blood more speedily 

 effected. 



The sections of the second and first pairs of maxilla 

 have become modified into delicate, leaf-like forms, in 

 which it is not as easy to distinguish the separate parts. 

 Care should be taken in removing the second pair of max- 

 illae not to injure the spoon-shaped organ (Fig. 8, />', c 2,?) 

 attached to each maxilla. This is marked with an inter- 

 rogation point, as it is uncertain whether it represents the 

 section h 4 or the united sections // 2 and h 4. This 

 organ is a hinged valve, and it pumps the water through 

 the -ill-chamber, whereby a fresh supply is induced to flow 

 in under the carapace. In the mandible (/;) the basal sec- 

 tion (// 1) is greatly developed, and the inner lobe is repre- 

 sented by the little jointed palp upon its upper side (h 3). 



Examining the large antenna (a 2), it is easy to detect 

 the basal section (// 1), with its long, slender, many-jointed 

 inner division (// 3) and scale-like outer division (A 2). An 

 opening (Fig. 9. /) will be seen on the ventral .side of the 

 basal section of both antennae. These are the outlets of 

 the two large '•green-glands' 1 which are situated within 

 the head, and are supposed to perform the function of 

 kidneys. In the little antenna (a 1) the inner and outer 



