I 



OF THE NEMATOIDS, PARASITIC AND FEEE. 575 



ehocephalus, and Trichosoma amongst the parasitic, and the remainder of the free Nema- 

 toids, its walls are more or less distinctly cellular, and no muscular fibres can be detected. 

 The Ascarides afford good examples of the simple muscular* oesophagus met with in 

 so many Nematoids, and its structure may at once be recognized by the examination of 

 their transverse sections (Plate XXV. fig. 3). We see then a circular section having a 

 thin structureless bounding wall, whilst internally there is a narrow triradiate cavity 

 bounded by a strong chitinous membrane, between which and the external walls are 

 seen on all sides a series of radiating close-set muscular fibres. By the simultaneous 

 contraction of these the narrow triradiate passage would be converted into a wide trian- 

 gular canal. If the plains of the radii were prolonged they would be found to alternate 

 in position with the cephalic lobes, one pointing to the mid-ventral region, and the two 

 others upwards and outwards in opposite directions. In certain Nematoids an appearance 

 of longitudinal bands is seen along the axis of the oesophagus. This is met with in the 

 genus Cvcullanus, and a transverse section (Plate XXVII. fig, 1 3, d) at once reveals their 

 nature, showing them to be produced by six thickenings of the internal chitinous lining 

 of the oesophagus. Similar formations exist among the free Nematoids, and are most 

 marked in Sphcerolaimus hirsutus. Two or three species of the genus Ascaris exhibit a 

 caecal prolongation of the oesophagus, extending backwards for a short distance along the 

 side of the intestine ; this I have seen in the so-called Filaria pisciumf of the Haddock, 

 and in Ascaris spiculigera, and it exists in other species. In these two animals also a 

 csecal prolongation of the intestine extends fonvards (Plate XXII. fig. 9 a & 6), whilst 

 in A. osculata the intestinal prolongation alone is present. Nothing definite can be said 

 concerning their use. In the genus Trilobus, amongst the free Nematoids, the three 

 lobe-like prolongations at the termination of the oesophagus seem to be developments of 

 much the same nature, and so also, in all probability, are the four glandular bodies in 

 the same region spoken of by De Qu.\trefages as existing in his genus Ilemipsilus. 

 The solid, though bright and almost homogeneous ring surrounding the oesophagus in 

 many of the free and some of the parasitic species has already been mentioned in 

 speaking of the nervous system. Amongst the free Nematoids it is very well marked 

 in the members of some of the marine genera, such as Leptosoniatum (Plate XXVIII. 

 fig. 33, b), Phanodenna, Symplocostoma^ and Oncholaivms. What its real nature may be 

 is quite problematical both to Eberth and myself It may be glandular, but no positive 

 statement can be made, save that it does not appear to belong to the nervous system. 

 In the land and freshwater species it seems absent altogether, and the same is the case 

 with a large proportion of the marine forms. Many Nematoids having a muscular oeso- 

 phagus present one or more swellings in its course. As a rule this swelling, when it 



• Although Professor Owbn in his ' Lect. on Comp. Anat.' 1855, p. 104, alludes without dissent to the 

 opinion expressed by CLoaTTBT, that " the thickened glandxdar parietes of the oesophagus in the Ascaris lumbri- 

 eoides may provide a secretion analogous to that of salivary organs." 



t This ammal, as it exists in the Haddock, at all events is a young Ascaris; reasons for this statement will 

 be advanced further on in the section on development. 



