LAND CRUSTACEANS. 



87 



in his work' on these organs in the Decapoda. They are afforded by the genera Porcellana 

 and Axius. A short duct leads from the gland to the opening at the base of the antenna. 



vi. The Nervous System (fig. 20). 



As might be expected, this shows a great general resemblance to that of the Pagurids- 

 the chief difference being in the greater concentration of the thoracic ganglia. The hrain 

 (1, fig. 20) is large, transversely elongated, and swollen at the sides. It gives off nerves to 



Fig. 20. Central nervous system of 

 Coenobita clypeatus from above with ab- 

 dominal chain removed. To the right an 

 enlarged view of the thoracic ganglion ia 

 shewn. 1. Brain. 2. Circumoesophageal 

 commissures . 3. Oesophageal ganglia. 4. 

 Transverse commissure. 5. Oesophageal 

 nerves. 6. Cerebral branch to the visceral 

 nerve. 7. Visceral nerve. 8. Thoracic 

 ganglion. 9. Nerves to the mouth-parts. 

 10. Longitudinal commissures. 11. Per- 

 foration for sternal artery. I — V. Nerves 

 to the legs. 



the eyes and antennae. The circumoesophageal commissures (2, fig. 20) are very long. For 

 the first part of their course they diverge and again converge in such a manner as to 

 enclose a long oval area, in the middle of which the oesophagus lies. At the hinder end 

 of the oval area a delicate transverse commissure (4, fig. 20) delimits it sharply. Behind 

 this point the circumoesophageal commissures converge much more gradually towards the 

 thoracic ganglion presently to be mentioned, finally running almost parallel for some distance. 

 Just in front of the transverse commissure there is a gentle swelling on each of the longi- 

 tudinal ones. These are the oesophageal ganglia (3, fig. 20) from which arise the two rather 

 large oesophageal nerves (5, fig. 20). These are joined by a fine nerve (6, fig. 20) which 

 runs backward in the median line from the brain — the three anastomosing in front of the 

 oesophagus. From their point of junction the median visceral nerve (7, fig. 20) runs up- 

 wards over the anterior wall of the stomach, to which organ it is distributed as in other 

 Decapods. 



The thoracic ganglion (8, fig, 20). In the Paguridae the thoracic ganglia are, with the 

 first abdominal, fused into an elongate mass in which, however, certain of the constituents 

 can still be made out, owing to the presence of constrictions in the mass and of perforations 

 to admit the passage of certain small arteries (besides the sternal artery). Coenobita shows 

 an advance on this in that the whole of the ganglia are fused into one oval body, through 



^ Marchal, " B^cherches...sur I'appareil excreteur des 

 CrustacBS Decapodes." Arch. Zool. Exper. (2), x. p. 57 

 (1892). See this work for the excretory organs of the Pagu- 



ridae (not Coenobitidae), Porcellana, and Axius. 



- 8ee Bouvier, Ann. Sci. Nat. (7), vii. p. 87 (1839). 



