ANATOMY 273 



The carapace is represented as transparent. The appendages have been removed, 

 but the outlines of the left entocoxites (6) have been sketched in. The positions 

 of the al)doniinal appendages are indicated by the external branchial muscles (17), 

 the branchial cartilages (19), the tendinous stigmata (18), and the abdominal endo- 

 chondrites (21). In the ceplialothorax (1) all the tergo-coxal and plastro-coxal 

 muscles have been dissected away, leaving the endosternite (11) with the occipital ring 

 exposed. One of the left tergo-proplastral muscles (4) and the left branchio-thoracic 

 nniscles (16) are represented. The longitudinal abdominal muscles are also seen. 

 All the muscles of the right side have been omitted except tlie haemo-neural muscles 

 (23), of which tlie last two are represented upon the left side also. At the base 

 of the telson the tiexors (29) and extensors (27) of the caudal spine are represented 

 as cut off near their insertions. The sphincter ani (26), levator ani, and occludor 

 ani (25), and their relations to the anus (28), are shown. 



The oesophagus runs forward to the proventriculus (3). Fi-om this the intestine 

 (20) passes posteriorly. 



The brain lies upon the neural side of the endosternite, and the ventral cord (22) 

 passes back through the occipital ring. The neural nerves are cut oft', but the 

 left haemal nerves and those from the fore-brain (12) are represented entire. 



The first pair of neural nerves go to the chelicerae. The second to sixth pairs go 

 to the next five cephalothoracic appendages, which are represented by the ento- 

 coxites (6). The seventh pair of neural nerves go to the chilaria, and the eightli 

 1-air to the operculum. The neural nerves from the ninth to the thirteenth arise 

 from the abdominal ganglia and innervate the five pairs of gills. 



From the fore-brain a median olfactory nerve (9) and two lateral ones (8) pass 

 forward to the olfactory organ ; a median eye -nerve (2) passes anteriorly and 

 haemally upon the right of the proventriculus (3) to the median eyes ; and a pair 

 of lateral eye-uewes pass to the lateral eyes (15). 



The first haemal nerve, or lateral nerve, follows the general course of the lateral 

 eye-nerve, but continues posteriorly far back on to the neural side of the abdomen. 



The haemal nerves of the hind-brain radiate from the brain to the margins of tin' 

 carapace, and each one passes anterior to the appendage of its own metamere. 

 The integumentary portions divide into haemal and neural branches, of which the 

 haemal branches (5) are cut off. Each haemal branch gives off a small nerve which 

 turns back toward the median line u]ion the haemal side of the body. 



The haemal nerves of the accessory brain pass through the occipital ring to the 

 sides of the body between the operculum and the sixth cephalothoracic appendage. 

 The seventh innervates the posterior angles of the ceplialothorax, the eighth the 

 opercular portion of the al)domen. The next five haemal nerves arise from the five 

 branchial neuromeres, pass out anterior to the gills to the sides of the abdominal 

 carapace, and innervate the first five spines upon the sides of the abdomen. 



Tlie first post-branchial nerve innervates the last abdominal spine ; the second 

 post-branchial nerve and one branch of the third post-branchial innervate the 

 posterior angles of the abdomen and the muscles of the telson ; and the caudal 

 branch of the third post-branchial nerve innervates the telson. 



Intestinal branches arise from all the haemal nerves from the sixth to the 

 sixteenth, and pass to the longitudinal abdominal muscles and to the intestine. 



Cardiac nerves arise from all the haemal nerves from the sixth to the thirteenth. 

 Six of the cardiac nerves conmumicate with the lateral sympathetic nerve (24), 

 which innervates the branchio-thoracic muscles (16). 



Two post-cardiac nerves ai'ise from the first two post-branchial nerves, and passing 

 to the haemal side anastomose with a branch from the last cardiac nerve, and inner- 

 vate the extensors (27) of the telson and the epidernns behind the heart. 



1, Cephalothorax ; 2, median eye-nerve ; 3, proventriculus ; 4, tergo-proplastral 

 muscles ; 5, haemal branch of integumentary nerve ; 6, entocoxites ; 7, 2nd haemal 

 nerve; 8, right olfactory nerve; 9, median olfactory nerve; 10, intestine; 11, 

 endosternite ; 12, fore-brain ; 13, origin of 4th neural nerve ; 14, lateral nerve ; 

 15, lateral eye ; 16, branchio-thoracic muscles ; 17, external branchial muscles ; 

 18, tendinous stigmata ; 19, branchial cartilages ; 20, intestine ; 21, abdominal 

 endochondrites ; 22, ventral cord ; 23, haemo-neural muscles ; 24, lateral sym- 

 pathetic nerve ; 25, occludor ani ; 26, s])hineter ani ; 27, extensors of telson ; 28, 

 anus ; 29, flexors of telson ; 30, lateral projections of abdomen ; 31, nerves of 

 spines : 32, external liranchial muscles. 



VOL. IV T 



