404 



ANIMAL RESPIRATION 



ing to a vanished gill), which is long and curved and can be 

 moved over the outer surface of the gills, serving apparently 

 to keep them clean (fig. 533). The epipods of the second and 



third foot-jaws project back under 

 the gills as " churning rods", help- 

 ing to maintain the circulation of 

 water. 



In the Mantis- Shrimps (Squilla, 

 &c.) the tail or abdomen is of rela- 

 tively large size, and tufted gills 

 are borne by the outer parts of its 

 limbs (fig. 534). It is a much 

 simpler arrangement than those so 

 far described. 



Sessile-eyed Crustacea, in which 

 the eyes are devoid of stalks, are 

 divided into Amphipods, flattened 

 from side to side, and Isopods, 

 flattened from above downwards. 

 In the former group are included 

 the little Sand- Hoppers (Talitrus, 

 &c.) and their allies, in which the gills are simple plates carried 

 on the inner sides of the limbs of the thorax (fig. 534). The 

 attenuated Skeleton- Shrimps (Caprelld] practically consist of head 



Fig- 533- Gills of a Crab 



The roofs of the gill-chambers have been removed 

 and four gills cut short on the left side: CL.R., clean- 

 ing-rods (epipod) of first foot-jaws, the left one is cut 

 short; CH.R., churning rods (epipods) of second and 

 third foot-jaws. 



Fig. 534. Gills of Mantis-Shrimp and Sand-Hopper 



A, Cross section through tail of a Mantis-Shrimp (Squilla), showing a gill on one side and a gill-axis on 

 the other. B, Cross section through thorax of a Sand-Hopper (Gammants], showing a pair of gills. 

 BK.P., Brood-pouch; D.GL., tubular digestive glands; HT., heart; INT., intestine; M.M., Muscles; N.C., 

 nerve-cord; ov., ovaries. 



and thorax only, the abdomen being reduced to a mere stump., 

 The thorax is made up of eight rings or segments (of which the. 

 two first are fused with the head), which is the typical number 



