428 



EPIZOA. 



form is entirely changed ; its senses, and means of relation with the ex- 

 ternal world, become atrophied ; singularly-formed excrescences sprout 



Nicothoe Astaci. 



from its sides ; and thus transformed, it is content to live beneath the 

 shell of the Lobster, without further intercourse with the external world 

 than is necessary to supply it with the blood which it sucks for food. 



(1106.) The mouth of the Nicothoe is a sort of membranous proboscis, 

 armed near its extremity with styliform points, with which it is enabled 

 to pierce the branchial membrane. Instead of the ordinary more or 

 less flexuous tube which constitutes the alimentary canal in other forms 

 of Entomostraca, the digestive apparatus of Nicothoe consists of two 

 wide sacculi, united together in the median line, in the shape of a horse- 

 shoe, from the centre of which a narrow canal proceeds towards the 

 mouth, constituting the oesophagus (fig. 223, 5), whilst, derived from 

 the opposite side, another tube of similar calibre runs backwards to 

 the termination of the tail, forming the intestine (c). The stomach, 

 therefore, is constituted by the two great lateral ca3ca (g, h), in the inte- 

 rior of which alimentary substances undergo their principal modifica- 

 tions ; so that these caeca are evidently analogous to what will be ob- 

 served in the Pycnogonidae ( 1112), with this difference, that in those 

 animals the caeca have penetrated into the interior of the ambulatory 

 claws. The thickness of the walls of these stomachal caeca is uniform 

 throughout; they are exceedingly delicate, only exhibiting in their 

 texture some small reddish cells, and are apparently connected to the 

 parietes of the body, in which they are loosely suspended by delicate 

 muscular fraena. 

 (1107.) One very remarkable circumstance presented by the alimentary 



