ON A NEW HISTIUOBDELLII). 313 



position the ectoderm is thicker than in most other situa- 

 tions, and in transverse sections a pair of nuclei are most 

 regularly to be observed in this thickened ai-ea; the double 

 row of cells which those represent would thus seem to form 

 a cord having the function of supporting the digestive canal. 

 The special developments of the coelomic epithelium in the 

 genital region will be described in the section on the repro- 

 ductive organs. 



The coelom of the head is almost completely cut off from 

 til at of the trunk by the muscular fibres of the neck constric- 

 tion and the gland cells that lie in that region. But this 

 separation is not complete, as evidenced by the fact that in 

 several female specimens sperms were found to have pene- 

 trated into this region. 



Nervous System. 



The nervous system (figs. 1 and 2) consists, like that of 

 Histriobdella as described by Foettinger, of a bruin, a pair of 

 oesophageal connectives, and a ventral nerve-cord with gan- 

 glia at intervals. The brain (figs. 1, 2, 6, 8), situated in 

 immediate relation to the integument of the dorsal surface of 

 the head, consists dorsally of a mass of nerve-cells {hr. c), 

 and ventrally of a mass of fibrillated material (br.f.). Of 

 the nerve-cells, special groups (tentacular ganglia) (fig. 6) 

 situated opposite the bases of the tentacles give off peri- 

 pherally nerve-fibres which run to the extremities of the 

 latter. The fibrous material is in the form of a curved 

 transverse band obscurely divided into two portions, anterior 

 and posterior. Running back from the main mass of the 

 brain at the sides of the oesophagus is a pair of processes 

 which are perhaps to be looked upon as representing the 

 visceral nervous system (''nerfs sympathiques " of Foet- 

 tinger) . 



The ventral nerve-cord consists of a strand of finely fibril- 

 lated material and groups of small nerve-cells similar to 

 those of the brain. In transverse section the fibrillated cord 



