TRICHOCEPHALUS. 71 



I conceive to be, to fix the head in its position when buried in the 

 mucous membrane in search of food." We are all agreed, there- 

 fore, as to the non-persistent character of this " collar," and I may 

 observe in passing, that this is not the only structural appearance 

 "which alters somewhat under varying circumstances, produced 

 either by agents directly affecting the worm itself, or by the manner 

 in which it is brought into view. 'Thus I may instance also the 

 very pecuhar longitudinal band which commences a little below 

 the head, and can be traced on one side of the neck the whole way 

 down to the commencement of the so-called body. This band, which 

 is remarkably distinct in fresh specimens, was first discovered by 

 Dujardin in T. dispar, and he states it to consist of prominent and 

 pointed papillse. Wedl, as I suspect, unknowingly referred to 

 it when speaking of certain Httle warts or spines passing round the 

 animal upon the epidermis ; but he also speaks of a band-hke 

 streak, which he compares to a structureless layer. Kuchenmeister, 

 on the other hand, goes so far as to aver his opinion that " the 

 streak is nothing but an optical phenomenon, but he, at the same 

 time, compares the httle prominences before-mentioned to the 

 hooldets present on the intromittent organ of the male. Accord- 

 ing, however, to my own observations, this band is a genuine 

 structure, and is made up of projecting, bluntly pointed, polygonal, 

 epidermal cells, which, in certain adjustments of the focus, refract 

 transmitted light so strongly that the band looks as if it consisted 

 of a regularly arranged series of pigment spots (Fig. 3, a) ; at 

 other times the centre of each cell becomes clear (a), and the 

 irregularly polygonal character of each individual cell is rendered 

 more apparent. On one side of the longitudinal band Dujardin 

 also figures and describes a series of minute superficial papilla, 

 which he associates with the festooned border of the band, but 

 these markings are manifestly referable to the subjacent convolu- 

 tions of the oesophagus. In the fresh condition of the worm, 

 moreover, the imbricated dermal rings (c, c. Pig. 3) are beautifully 

 distinct. These annulations do not extend all round on the 



