NOTES ON PARASITES. 



AMONGST the many doubtful points which have ex- 

 ercised the minds of those Zoologists who work at 

 the parasitic worms, none has caused a greater divergence 

 of opinion that the question of the existence or non-existence 

 of an external epithelium. Since Rindfleisch and shortly 

 afterwards A. Schneider, some thirty years ago, denied that 

 such a layer existed, hardly any two writers have agreed as to 

 the nature of the skin of Cestodes and Trematodes. All, 

 however, have recognised the existence of a cuticle, but as 

 to its nature there were almost as many opinions as there 

 were writers. Rindfleisch and A. Schneider regarded it as 

 the basement membrane of a lost epithelium, and this view 

 was adopted by Leuckart and consequently gained a wide 

 acceptance ; other writers, however, held that the cuticle 

 was itself the external epithelium which had become much 

 modified and had lost all trace of cells and nuclei. 



The recent researches of Professor Blochmann ^ of 

 Rostock have done much to clear up this and many other 

 doubtful points in the histology of the Cestodes and Tre- 

 matodes. These researches have been largely facilitated 

 by the employment of Golgi's method of staining and by 

 the use of the Iron-haematoxylin staining fluid : they 

 were chiefly carried out on Ltgnla vwnogramma, though 

 twelve other species of Tape-worm and many Trematodes 

 were also investigated. 



Blochmann begins his paper by pointing out that if there 

 is no external epithelium we must invent a new name for 

 the cuticle, since it is of the essence of a cuticle that it 

 should be formed from the free ends of epithelial cells ; 

 secondly, that external unicellular glands such as are com- 

 mon in Trematodes and also occur in Cestodes, though less 

 frequently, are as a rule produced by the modification of 



^ Die Epithelfrage hei Cestoden unci Tre/natoden, Hamburg, 1896. 



