XI 



PHYLUM ARTHROPODA 



579 



salivary glands, opening on the labrum, have been found in several 

 genera. 



In most of the Branchiopoda, Ostracoda, Copepoda, and 

 Cirripedia, respira- 

 tion takes place by 

 the general surface 

 of the body, and the 

 only respiratory 

 organs are speci- 

 ally modified parts 

 of the appendages. 

 In the stalked 

 Barnacles, how- 

 ever, there are 

 delicate processes 

 attached to the 

 feet, which are 

 supposed to be 

 rudimentary gills. 

 Amongst the Mala- 

 costraca also, the 

 Phyllocarida, 

 many Mysidacea, 

 and the Cumacea 

 have no special- 

 ised respiratory 

 organs, but the 

 Euphausiacea 

 possess tufted 

 p o d o b r a n c h i se 

 (Fig. 479) quite 

 uncovered by the 

 carapace. In the 

 Decapoda the gills 

 may be either 

 plume-like, as in 

 Astacus and its 



allies, Or the SOlt p IQ. 473. Orchestia cavimana, male, a, eye ; ai, antennule; 



cylindrical gill- 

 filaments may be 

 replaced by flat 

 plates, as in Crabs 

 and many Prawns. 

 It is in this order 

 only that we find the three types of gill described in Astacus, 

 and the examination of numerous forms leads to the conclusion 

 that the typical or theoretical branchial formula for the group is 

 as shown in the table on page 580. 



ed 



2, antenna ; aoa, anterior aorta ; aop, posterior aorta ; bm, ventral 

 nerve-cord ; br, gills ; C+ T, cephalothorax ; de, vas deferens ; ed, 

 rectum ; ehd, entrance of excretory caecum into intestine ; g, 

 brain ; h, heart ; M, excretory caecum ; l-f, maxillipede ; I, 

 digestive glands; od, anterior part of gon ad in which small ova 

 are often found in young males; oe, gullet; Pi #7, abdominal 

 segments ; sm, "stomach " ; ud, intestinal caecum ; vs. vesicula 

 seminalis ; t, testis ; II VIII, free thoracic segments. (From 

 Lang's Comparative Anatomy, after Nebesky.) 



