DRACUNOULUS MEDINENSIS. 379 



Be that as it may, the above-mentioned characteristics come out 

 more cogently when we submit the worm to microscopic investiga- 

 tion. Under low powers, the head displays a rather flatly- convex 

 outline, near the centre of which four papillae, or rudimentary ten- 

 tacula, project at equidistant intervals from one another, and from 

 the centrally-placed oral aperture. These spiaules, as they have 

 been termed, were described long ago by several authors, but not 

 so accurately as has been done by Bastian, who observes that the 

 two vertical papUlge are much larger than the others, and also 

 nearer the oral aperture, " whilst the two lateral, more remote from 

 the mouth, not prominent, and scarcely more than opaque spots, 

 are situated at the commencement of the gradually- widening, late- 

 ral, intermuscular spaces." As my own examinations of Sir George 

 Ballingall's specimens of Dracunculus were made many years ago, 

 and as, with the exception of drawings of the young, I have no 

 trustworthy record of my dissections, I shall on several points rely 

 on Bastian' s very careful description of the adult worm. The 

 papillae in question are situated, moreover, within the limits of a 

 quadrangular space, from whose borders the four great longitudi- 

 nal dorso-ventral muscles apparently take their origiu. Respecting 

 these muscles little need be said, since in all their essential features 

 they correspond with those of other nematoda, and terminate in 

 the so-called caudal appendage. As regards the integument, this 

 consists of two distinct and easily- separable layers, an external 

 thick, transparent, cuticular, chitinous investment, and an internal 

 thin, granular layer. The external layer, according to Bastian, is 

 itself separable into two portions, the outer being thick, " tough, 

 elastic, transparent, and perfectly structureless, save that it pre- 

 sents transverse markings at intervals." The surface itself is per- 

 fectly smooth, " there beiug no appreciable depressions correspond- 

 ing to the annulose markings such as may be seen to a sHght 

 extent in Ascaris lumbricoides and A. mystax, but there is some 

 considerable alteration in the refractive power of the membrane in 

 these situations, as when seen a little beyond the proper focal dis- 



