430 



provided with those enormous aliform appendages that are so cha- 

 racteristic of the female adult Nicothoe. 



(1111.) PYCNOGONIDJE. In the Pycnogonidae*, the aperture of the 

 mouth is found at the extremity of the tubular proboscis which projects 

 from the anterior part of the body of these remarkably- constructed 

 animals, and which, from its general conformation, certainly reminds 

 us more of the Acaridiform Arachnidans than of the Crustacean type of 

 structure. The oesophagus is an extremely delicate and slender canal 

 which passes directly backwards into the cephalothorax, where it at 

 once expands into a central digestive cavity or stomach which occupies 

 the centre of the body, and terminates posteriorly in a very narrow and 

 rudimentary intestine. 



(1112.) From the circumference of the stomach are given off ten long 

 caeca, the disposition of which is remarkable : of these, the two anterior 

 are prolonged forwards to the pincer-like rudimentary foot-jaws or palpi, 

 into the interior of which they penetrate for some distance ; while the 

 remaining four pairs, which are of great length, are continued in a 

 similar manner into the locomotive or thoracic legs, extending almost to 

 the end of the antepenultimate joint. The anal orifice of the intestine 

 is situated, as usual, at the extremity of the very rudimentary abdomen. 



(1113.) When distended with fluid, these ca3ca may be observed to 

 become constricted opposite to each articulation of the limb. Their 

 structure is exceedingly simple ; indeed, they seem to consist of a very 

 thin diaphanous membrane, in which no trace of fibre is distinguishable, 

 but which externally seems to be crusted over with a granular opake 

 substance, sometimes presenting a violet or yellowish tint. These 

 granulations are more thinly scattered over the stomach than over the 

 cseca, and upon the intestine they are wanting altogether. The whole 

 of this digestive apparatus, notwithstanding that its walls contain no 

 perceptible fibres, is contractile, and floats freely in the general cavity of 

 the body, being only retained in situ by a few delicate frsena ; its dif- 

 ferent parts may be observed to have alternate movements of contraction 

 and dilatation, driving, in undulations, first in one direction and then in 

 another, the liquid which they contain. This liquid, which is quite 

 transparent, hurries along with the materials in process of digestion. 

 These generally present themselves under the appearance of roundish or 

 ovoid masses, about ^th of a millimetre in diameter, smooth and entirely 

 without granulations during the earlier period of the digestive process ; 

 but as digestion advances, they may be seen to become decomposed into 

 roundish granules that powerfully refract the light, and which are 

 scarcely -g-J-jjth of a millimetre in size. The faeces seen in the intestine 

 are entirely made up of these granules irregularly agglomerated toge- 

 ther ; and it is rare to find among them any traces of alimentary sub- 

 stances which are not entirely decomposed. 



* Vide M. de Quatrefages, Ann. des Sci. Nat. 1844, iv. p. 72. 



