48 



PARASITES OF MAN 



between the cilia of the head and body respectively. The former 

 are at all times vibratile, active, and conspicuous, whilst the 

 latter are more delicate, capable of comparatively little motion, 

 and partaking more of the character of fine setae. In length 

 their general measurement varies from 5" to 5000"' ^ ne a tion 

 of pure sea-water on the free animalcules, previously immersed 

 in fresh or brackish water, was equally striking. All, without 

 exception, immediately became paralysed and almost motionless ; 

 nevertheless, on again adding fresh water, several entirely reco- 

 vered. It is worthy of notice that in these cases the cephalic 

 cilia furnished the first indications of returning viability. I was 

 particularly struck with the behaviour of one embryo, which, 

 under the stimulus of the sudden shock, retracted its cone- 

 shaped head almost entirely within the general cavity of the body 

 (fig. 14, lower specimen) . In their moribund condition, whatever 

 shape the embryo retained, the sarcodic contents gradually faded 

 away ; the outline of the creature, however, becoming more 

 marked (fig. 16). Usually the body of the animalcule became 

 elongated whilst expiring in sea-water. Under other circum- 

 stances the embryo frequently bursts ; the sarcodic contents 

 escaping in the form of amoeba-like bodies and the cilia retain- 

 ing their powers of movement long after all traces of the 

 sarcode have disappeared. 



The larvae of Bilharzia closely resemble those 

 of Fasciola hepatica, which latter may be appro- 

 priately noticed in this place. The ciliated em- 

 bryo of the common liver fluke has the form of 

 a long cone inverted ; the anterior end or head 

 being flatly convex. In the centre is a short 

 proboscis-like papilla destitute of cilia (fig. 17). 

 The general covering of cilia rests on a well- 

 defined granular epidermis; this latter being 

 succeeded by a dense peripheral layer of large 

 nucleated cells, each of them measuring about 

 53-" in diameter. The epidermis measures g^ D " 

 in thickness. In the central mass of paren- 

 chyma no internal organs are recognisable, but 

 Leuckart observed indications of a canal which 

 he thought might open at the tail, though the 

 opening itself was not actually visible. 

 As long as the ciliated covering remains intact the embryo, 

 like other animalcules, displays great activity, whirling round 



FIG. 17. CiliHted em- 

 bryp of Fasciola he- 

 patica, showing tlie 

 so-called eye-spot. 

 After Leuckart. 



