156 BULLETIN OF THE 



cell-rows. There certainly are no transverse cell walls and no very 

 regular distribution of nuclei ; and while they may be potentially equiv- 

 alent to rows of cells, they certainly are not ther same as the structures 

 in the Trichotrachelidse known as cell-rows. To use the expression, 

 then, is to emphasize a morphological relationship which, if it exist, is 

 much more distant than the use of this word would lead one to sup- 

 pose. Biirger also described the regions of the intestine bounded suc- 

 cessively by four, three, and two cells; but in spite of his strongly 

 expressed doubts on the subject, he was led to regard the terminal 

 orifice of the papilla as the anus, following the description of Verrill 

 and Fewkes. It must have been poorly preserved material which gave 

 the appearances shown in his Figures 25 and 29, for I am convinced 

 that the supposed cuticular lining of the intestine does not exist, I have 

 found nothing which supports his claim, set forth at length, that the 

 intestinal lumen when apparently bounded by three cells is really 

 formed at the expense of only one, and belongs to that cell alone. 



3. Anterior Chamber. 



The anterior chamber is a prominent and characteristic feature of the 

 anatomy of Nectonema. Even in the living animal one can usually dis- 

 tinguish its main features (Fig. 3) under a compressor. The semi- 

 transparent area extends as far as the transverse partition which, at 

 about 0.3 to 0.4 mm. from the apex of the head, cuts off this portion 

 from the general body cavity. In the living animal this partition is 

 concave anteriorly, and apparently slightly thicker at the centre ; on 

 sections it is seen to be covered on its anterior face by a thin peritoneal 

 membrane, whose flattened nuclei (Plate VII. Fig. 95) may be easily 

 discerned at intervals. I am not sure that this same peritoneal mem- 

 brane lines the entire anterior chamber. It can easily be demonstrated 

 over the lateral surfaces and around the oesophageal cell, where similar 

 nuclei may be demonstrated even under the dorsal commissure of the 

 brain and farther forward. On the dorsal surface of the brain I have 

 searched in vain for the nuclei or the membrane ; yet it is equally im- 

 possible to find where it stops, if it does not line the entire chamber. 



In alcoholic specimens much of the regular character of the partition 

 is lost, and it is usually found to be more or less distorted, as the effect 

 of the various processes through which the material has passed. The 

 fibres of which it is composed run in all directions, chiefly radiating 

 from the centre toward the body wall. They show frequent pale nuclei 

 (Fig. 95). The partition is pierced by the oesophagus alone, and it 



