80 A FURTHER KNOWLEDGE OF THE CYSTIC CESTODES, 



indicative of the stage of development of the scolex. In this stage 

 the three parts into which, after Lang,* the adult scolex can be 

 divided can readily be distinguished. These parts are : (1) The 

 anterior or head region, which carries the bothridia ; (2) The 

 middle or neck region, through which run the proboscis sheaths ; 

 (3) The posterior region, in which the proboscis bulbs are situated. 

 The internal parts, however, are still in process of differentiation, 

 and the cuticle investing the scolex is still a comparatively thin 

 layer. 



In the posterior part of the scolex the proboscis bulbs are 

 represented by non-staining tracts apparently of a fibrous nature 

 and surrounded by deeply staining cells. Such cells occur along 

 the whole course of the proboscides and sharply mark them oflT 

 from the surrounding cells. In the middle region of the scolex 

 occur longitudinally running cellular strands surrounded by deeply 

 staining cells similar to those round the bulbs. These cellular 

 strands jirobably give rise to the retractor muscles of the probos- 

 cides, while the deeply staining cells form the sheaths of the 

 proboscides. Anteriorly the proboscides themselves (Fig. 17, 

 prb.) are seen to be hollow structures with well-defined cuticular 

 walls and surrounded by deeply staining cells. On the interior 

 of the hollow proboscis the hooks appear as small inwardly-pro- 

 jecting conical processes of its cuticular wall. 



In sections of a cyst slightly older than the preceding, the 

 proboscis bulbs are now found to possess very definite fibrous 

 walls, enclosing a cellular strand, from which the retractor muscle 

 will be developed. The wall of the bulb is very much thicker on 

 its inner face than externally and closely surrounds the cellular 

 strand, the large cavity found in the bulb of the fully-formed 

 scolex being not yet formed. The proboscis, suirounded by a 

 layer of dee|)ly staining rounded cells, is now found to lie in a 

 definite cavity, the cuticular wall of which forms the proboscis 

 sheath. Posteriorly the sheath becomes continuous with one of 



* MT. Zool. Stat. Neap. ii. 1881, pp. 372-400 ; see resume, Journal of the 

 Royal Microscopical Soc. 2ud Ser. Vol. ii. part I, 1882, 51. 



