364 



BIOLOGY. 



[Book vi. 



most of the articulated invertebrates (worms, annelates, arthro- 

 pods), especially when the lateral cords approach each other on 

 the ventral face, as is the case with some species. 



According to M. Blanchard, the nematoids (ascarides, strongyli 

 filarians, and so on) have, at the origin of the oesophagus, four 



Fig. 56. 



A , nei-vous system of Serpnla contortv^licata ; a, pharyngian ganglions superior ; 6, inferior ; 

 6', ventral trunk ; n, nerves of the mouth ; t, nerves of the antennse. 



B, nefvous system of Nereis regia : o, eyes reposing on the (Bsophagiau ganglion superior. 

 The other designations as in the preceding figure. 



small ganglions, situated two at the right, two at the left, a.nd 

 connected by commissures forming an cesophagian collar. 



This cesophagian collar is found in all the annelates and arthro- 

 pods, but it is usually formed of a super-oesophagian ganglionary 



