2()6 



THF, CRAYFISH. PHYLUM ARTHROPODA 



the head, and a pair of antennary arteries, which start one on 

 each side of the ophthalmic, run forwards and outwards, and divide 

 each into two branches, one gastric and the other to the antennae 

 and green gland. Behind and below the antennaries arise a pair 

 of hepatic arteries, which supply the liver, and from the hinder 

 angle of the heart there is given off a vessel that at once divides 

 into a dorsal abdominal artery, which runs backwards above 



hi 



od. 



d.atp-S. extm. 



heg.Q 



Fig. 138. — The internal organs of a female crayfish in situ. Slightly diagrammatic. 



a.g.m.. Anterior gastric muscle; an., anus; ant.a., antennary artery; at.i, antennule ; at.2, antenna; 

 bl.g., bladder of the green gland ; e.g., cervical groove ; c.oes., circumoesophageal commissure ; cer., 

 cerebral ganglion ; ch., cheliped ; cm., caecum ; d.ab.a., dorsal abdominal artery ; en.sk., endophragmal 

 skeleton ; eye ; ext.m., extensor muscles ; fl.m., flexor muscles, looping from one sternum to another 

 over v.l.m. ; g.gl., green gland ; h.g., hind-gut ; hep.a., hepatic artery ; ht., heart ; Ir., liver ; Ibr., labrum ; 

 md., mandible ; m.p., mandibular palp; o.b., opening of bile duct ; od., oviduct ; ces., oesophagus ; 

 op.a., ophthalmic artery ; os., ostia ; ov., ovary ; p.g.m., posterior gastric muscle ; pern., pericardium : 

 prv., proventriculus ; rst., rostrum ; st.a., sternal artery ; st.ab., abdominal sterna ; st.h., sternal region 

 of the body in front of the mouth ; st.th., thoracic sterna ; t.g., tubercle for green gland ; tg., terga ; 

 v.l.m., ventral longitudinal muscles ; v.n.c, ventral nerve cord ; w.l.^, last walking leg. 



the intestine and supplies it and the muscles of the abdomen, 

 and a sternal artery. This passes downwards, through an opening 

 in the ventral nerve cord, and divides into a backward-running 

 ventral abdominal and a forward-running ventral thoracic artery, 

 by which the limbs are supplied. Each of the arteries branches 

 many times, till it finally gives rise to minute vessels in the organs 

 it supplies, but there are no capillaries. 



From these vessels the blood passes into great sinuses which 

 surround the organs. The largest of these is the perivisceral 

 cavity, but there are also blood spaces in the limbs and elsewhere. 

 The blood from the limbs and a great part of that from the 

 perivisceral cavity is gathered up into a sternal sinus, which lies 



;i tunnel formed by the endophragmal skeleton and contains 



