KEIMARKABLE SPECIES OF ECHIÜROIDS. 21 



On account of tlieir presence the muscular layers of the body- 

 wall appears divided into five broad longitudinal zones, 



A short distance (1-1.3 cm.) behind the mouth there exist 

 a pair of moderately long ventral hooks. These are gently curved 

 mediad and are of a bright yellow color. 



Some Points of the Internal Structure. 



Figs. 18 and 19 in PL II. and fig. 23 in PI. III., all drawn 

 from dissections of the worm, will serve to give a general idea 

 of the arrangement of internal organs. For study of the micro- 

 scopic structure were employed material which were fixed with 

 either saturated corrosive sublimate solution or Flemmtng's strong 

 solution. Heidenhain's iron-hsematoxylin or Delafield's hsemat- 

 oxylin was used for nuclear stain, and several anilin pigments 

 for plasma stain. In the following description, I will first take 

 up the body proper, leaving the proboscis to be dealt with last. 



The Body-wall. — In the living state of the worm, this is 

 relativelv thin. It o-rows somewhat thicker towards both ends 

 of the body, where the surface is beset with largest papillse. It 

 may be said to be made up of five distinct layers, viz., the cuticle, 

 the epidermis, the cutis, the muscular layer and the peritoneum 

 (fig. 26). 



The cuticle, which forms the outermost covering, is moderately 

 thick (figs. 27 and 28, ct.). As was pointed out by Jameson 

 ('99) in Thalassema neptuni, it is composed of an outer deeply 

 and an inner less deeply staining layer and of the innermost 

 alveolar layer. 



The e2yidermis is represented by a single-layered epithelium 



