350 OBSERVATIONS ON THE CHLORAEMIDAE, 



for some distance further back in the form of two comparatively 

 narrow tubes, which lie close together on either side of the middle 

 line of the dorsal part of the body-qavity. Their ducts meet in 

 front below the oesophagus, and the median duct thus formed 

 appears to open on the ventral aspect of the praestomium, but 

 defects in the sections leave this doubtful. The glands are lined 

 with an epithelium of large irregularly-shaped cells (tig. 22) with 

 vacuolated protoplasm containing numerous rounded granules of 

 various sizes, some of which are stained darkly by haematoxylin, 

 the largest having the appearance of being made up by the coales- 

 cence of numerous extremely minute particles. 



In Stylarioides miotics these glands are in the form of narrow 

 twisted tubes, the cells lining which are similar to those just 

 described. The granules do not become stained by borax-carmine 

 and a nucleus becomes revealed in each cell. In Siphonostomum 

 affine the cells have the form represented in figure 23, mostly 

 narrow at the base, with a rounded bulging at the free extremity, 

 containing numerous minute granules scattered through their 

 protoplasm and some larger ones at the base, where there is in 

 most a zone of protoplasm which stains more deeply with haema- 

 toxylin than the rest. 



VII. — Nervous system, eyes, and tentacles. 



The remarkable position occupied by the ventral nerve-chain in 

 the members of this family was remarked upon by Leuckart in his 

 account of Siphonostomitm vaginiferum, Kathke (I.e., p. 165). It is 

 completely separated from the epidermis, and lies within the layer 

 of circular and oblique muscular fibres of the body wall. The 

 cord presents very distinct ganglionic swellings, which are bilobed 

 externally, though completely fused internally ; between the 

 ganglia the cord is distinctly double. The oesophageal commis- 

 sures are of great length in co-ordination with the retractility of 

 the prse- and peristomia. The anterior part of the nerve cord in 

 Stylarioides ductus is represented in plate xxviii. fig. 24. 



The presence of eyes in members of this family has frequently 

 been overlooked owing to the retractile character of the praesto- 



