84 



L. A. BOERADAILE. 



freely. The axis is attached at one point to the side of the thorax, and there the blood 

 enters it. The lamellae diminish in size towards each end of the axis, whereby the whole 

 gill becomes spindle-shaped. The gill-formula is as follows': — 



The arrangements for the supply of blood to the gills consist, as usual, of afferent 

 branchial vessels, arising from the sternal sinus, and of efferent vessels leading to the 

 pericardial sinus and so to the heart. 



The lining of the hranchiostegite is a thin, smooth membrane. There is no spongy 

 tissue such as is found in Ocypode or vascular tufts as in Birgus. According to Bouvier-, 

 blood enters the hranchiostegite from the large sinus which encloses the stomach, and leaves 

 by the great vein, which may easily be found at the hinder edge of the organ. This 

 starts in front as a small vessel and runs backward round the lower edge of the hranchio- 

 stegite, enlarging as it goes. Finally it curves inwards with the hinder edge of the 

 hranchiostegite and, when this rejoins the body, passes on to the pericardium. I did not 

 find it possible by injecting this vessel to irrigate any definite plexus in the hranchio- 

 stegite. The coloured fluid passes with great readiness into the space between the strong 

 outer and the delicate inner wall of the organ, but it is here contained in a loose and 

 irregular system of lacunae, or rather in a single cavity divided by strands of tissue. 



The gill chamber. Provision for moistening the gills. The third leg in its normal 

 position, pressed up against the soft hranchiostegite, indents the latter in such a way as 

 to limit the branchial chamber to a comparatively small region in the hinder and upper 

 parts of the thora.x. This chamber is widely open behind, so that the gills can generally 

 be partly seen without lifting the hranchiostegite. The animal seems to be able to in- 

 crease this opening at will, but over the greater part of their surface the hranchiostegite 

 lies fairly close above the gills. There is thus no attempt at the formation of anything 

 like a lung. The free edge of the hranchiostegite is incurved, and the trough thus 

 formed is lined with hairs and usually very moist. Another hairy surface, possibly of im- 

 portance in the retention of water, is to be found on tlie wall of the thorax above the 

 gills, between them and the origin of the hranchiostegite. 



' The gill-formula of Piujurus is the same as that of - Bouvier, C. Rend. ex. pp. 1211 ff. (1890). My observa- 



Coenobita save that the gills on the third maxilliped aud first tions, wLiich contirra those of Bouvier, were made when I waa 



leg are better developed. Eupagurvs differs in having only in ignorance of his researches on the blood supply of the 



one pleurobranch — that on the fourth leg. hranchiostegite. 



