432 



ARTHROPODA. 



by numerous blood-vessels. In Birgus latro the gill chamber is 

 divided into two portions (fig. 438), the upper part being pulmo- 

 nary, the lower containing the reduced gills. 



FIG. 438. Diagrammatic section through Birgus latro, showing lungs. (From Lang, 

 after Semper.) a,, a 4 , afferent blood-vessels : ah, pulmonary chamber; ek, el, el' % 

 efferent blood-vessels ; ft, heart; k, gills ; kd, branchiostegite ; p, pericardium. 



C 



bl... 



FIG. 439. Anatomy of Crayfish (Astacus). A, dorsal surface removed ; B, scheme 

 of circulation ; C, viscera removed, showing green gland and nervous system. a, 

 anus ; oa, hepatic artery ; ae, antenna ; az, antennula, also sternal artery ; am, 

 muscles of stomach ; o, ophthalmic artery ; op, abdominal artery ; av, ventral 

 artery; bl, urinary bladder; ftr, gill arteries; c, oesophageal commissures; gd, 

 green gland; 0n', brain ; .qr?i 2 - 13 , ganglia of ventral chain; ft, heart; hd, intes- 

 tine ; fc, mandibular muscles ; I, l\ liver and its duct ; w, stomach ; o, otocyst ; 

 oes, oesophagus ; on, optic nerve ; pc, pericardium ; sgn, sympathetic nerve ; t, t', 

 unpaired and paired portions of testes ; t?, ventral blood sinus ; vd, vas deferens ; 

 vdr, vems from gills to heart. 



