184 BULLETIN OF THE 



contractile portion. If now we conceive this plasmatic portion to he 

 reduced to a minimum, the form of muscle cell characteristic of Gordius 

 will be reached; for in this genus the projecting protoplasmic portion is 

 entirely lacking, the layer of contractile fibrillse surrounds the entire 

 cell, and the nucleus is found in the thin strip of plasma which occu- 

 pies the centre. Not only do we find in a typical Coelomyarian cells 

 in which the plasmatic cell body hardly projects beyond the contrac- 

 tile layer, but I have also been able to find in cross sections of Gor- 

 dius sp. ? certain regions where the fibrillar layer in the proximal 

 portion of the cell differs in thickness and in refractive power from that 

 in the distal portion. I do not believe, therefore, that the difference in 

 the muscular systems is so great as has been maintained. 



To consider the second objection urged by Burger against the rela- 

 tionship of Gordius and Nectonema, namely, the structure of the intes- 

 tine, it will be necessary to make a short digression to consider the 

 structure of the alimentary canal, and especially of the oesophagus, in 

 Nematodes. Most text-books recognize only one type of oesophagus in 

 this group, a muscular organ with a more or less triangular lumen 

 lined with chitin, from which muscle fibres radiate perpendicularly 

 to the long axis of the tube. This organ evidently acts like a suction 

 pump in taking up nourishment. 



If, however, one examines the literature on the group, it is evident that 

 there are a number of families to which this description will not apply, 

 and that there is really a second well marked type of oesophagus. This 

 consists of a minute chitinous tube extending through a cell, or row of 

 cells, with which no muscle fibres ai-e connected. Evidently there is here 

 no means of varying the size of the lumen. I believe the oesophagus in 

 every family of Nematodes may be reduced to the one type or the other. 

 The larger number of forms show the first, but in the Trichotrachelidse 

 and Mermithidse the oesophagus is constructed on the second type, as is 

 also the case in Nectonema. In Gordius this organ is found to be highly 

 degenerate, and in certain species, or in specimens of a certain age, has 

 entirely disappeared. Its condition appears to be different according to 

 the descriptions given ; but in a specimen collected in Cambridge there 

 is absolutely no trace of an oesophagus in a perfect series of transverse 

 sections. From the account of Vejdovsky ('86, p. 404) it is at once evi- 

 dent that the oesophagus does not belong to the first type, and according 

 to his description ^ and figures ('86, p. 404, Taf. XV. Fig. 35) it bears a 



1 Vejdovsky says (p. 404) : " Als MunJhohle bezeichne ich das engeKanalchen," 

 etc. It is this portion of the alimentary canal which I regard as the morphological 

 equivalent of the oesophagus of the second type. 



