21 G 



IT. GRAHAM CANNON 



vary in size, being smallest at the base of the first antennae and 

 largt^st about the centre of the group. The nuclei are usually 

 about 20^ long, but the smallest are never less than half this 



Text-fig. 1. 



umll 



iSemi-diagrammcatic ventral view of Siniocephalus vetulus. 

 The thick dotted lines ending in arrow heads on the animal's 

 left side indicate tlie direction and extent of the normal move- 

 ment of the appendages figured on that side.) adg, anterior 

 pair of distal gland-cells ; ant 1. first antenna ; ant 2, second 

 antenna ; C(K connexion between anterior and posterior pairs 

 of distal gland-cells ; en 3, proximal endite of third trunk-Umb ; 

 ex 2, exopodite of second trunk-limb ; gn 2. gnatho-base of 

 second trunk-limb ; k 1, k 2, k 3, branchiae of first, second, and 

 third trunk-limbs respectively ; Z, labrum ; w^f>, mandible ; ni.r, 

 maxilla ; ixly, posterior pair of distal gland-cells ; pg, proximal 

 gland ; // 1, 11 2, tl 3. first, second, and third trunk-limbs 

 respectively. 



length. For comparison it may be stated that the length of 

 the nuclei of nerve-cells or of muscle-cells, which are of very 

 uniform size and oval shape, is 4fx. Thus the volume of these 

 large gland-cell nuclei must be many times, at least twenty 



