ON A PRORHYNCHID TURBELLARIAN. 637 



the intestinal cells of Turbellaria in general. The epithelium 

 is supported by a thin layer of a fibrous character, apparently 

 muscular, containing numerous spindle-shaped nuclei. 



Nervous System. — The brain (fig. 1) consists of two large 

 ganglia situated near the anterior extremity of the body above 

 the mouth, and connected together by a thick commissure; 

 the nerve-cells are mainly confined to the ganglia, to which 

 they form a thick investment. Given off from the brain on 

 each side is a large nerve passing to the corresponding ciliated 

 sac. Two main longitudinal trunks (figs. 1 and 2) are given 

 off on each side posteriorly. One of these, which is much the 

 smaller, runs in the lateral flange of the body.^ It gives off 

 regularly arranged transverse branches, of which those on the 

 inner side join corresponding branches of the larger trunk, 

 thus giving rise to a number of commissures connecting the 

 two trunks together, while those on the outer side given off 

 opposite the commissures run outwards towards the lateral 

 margin, giving off branches to the integument. In addition 

 to the commissures which connect it with the smaller trunk, 

 the larger nerve-cord gives off on its inner side many trans- 

 verse branches running in the ventral wall of the body ; 

 whether these form complete commissures was not ascertained. 

 The ciliated sacs are two deep excavations, each situated just 

 behind the corresponding anterior angle of the body, and 

 opening on the ventral surface near the lateral border by a 

 wide orifice. The cavity is lined with a layer of regularly 

 arranged, large, columnar cells, beset at their inner extremity 

 with long cilia. Internally and posteriorly the ciliated sac is 

 prolonged into a narrow cylindrical tube, which, after 

 receiving the ducts of a number of unicellular glands 

 similar to those that discharge on the outer surface, ends 

 blindly. In close contact with the columnar cells of the 

 sac, and probably in continuity with them, is a layer of 

 nerve-cells, processes from which go to form the nerve already 

 referred to. 



^ The lateral cords have been made too thick in fig. 1, and made to run 

 too far back. 



