PYCNOGONID^E. 431 



(1114). It has been stated above, that all that portion of the alimen- 

 tary canal which intervenes between the oesophagus and the intestine is 

 free, and floating loosely in the general thoracic cavity, which cavity is 

 prolonged into the limbs extending beyond the terminations of the 

 caeca ; and in this cavity it is easy to distinguish the muscles subser- 

 vient to locomotion, and which, more especially in the limbs, line, as it 

 were, all the interior of the different joints, so that the digestive appa- 

 ratus is evidently lodged in a great lacuna or cavity which occupies the 

 entire thorax, and is prolonged into the claws. This lacuna is filled up 

 with a transparent fluid, in which may be distinguished a great number 

 of irregular transparent corpuscles, which appear to consist of agglome- 

 rations of smaller globules. The fluid is constantly agitated with irre- 

 gular movements backwards and forwards, which are determined by the 

 general movements of the animal, or by the alternate contractions and 

 dilatations of the stomach and caeca, and which constitute all the circu- 

 lation which is discernible in these creatures. No organ is detectible 

 specially appropriated to this function ; heart and blood-vessels are alike 

 wanting, the great lacuna above described taking the place of both, 

 since the fluid which it contains is evidently the representative of the 

 blood, or, rather, it is the blood itself. Neither are there any special 

 organs appropriated to respiration, which is here evidently carried on by 

 the general surface of the body, as we have found it to be in many of the 

 Entomostracous Crustaceans. 



(1115.) The remarkable disposition of the alimentary canal so con- 

 spicuous in the Pycnogonidse, and which exists, to a greater or less 

 extent, among the inferior tribes of various classes of animals, has been 

 named by M.de Quatrefages " phlebenterism," from the circumstance that 

 in the instance above given, and in many similarly- organized creatures, 

 the intestinal ramifications supersede, to a greater or less extent, the 

 functions of the* circulatory, respiratory, and chyliferous systems of the 

 higher animals. 



(1116.) The nervous system of the Pycnogonidae consists of a thoracic 

 chain of ganglia, from which are derived the nerves supplying the 

 limbs, and of a supra-oesophageal mass, giving off the optic nerves to 

 form the minute ocelli that constitute the visual organs of these extra- 

 ordinary creatures. 



