1 8 WRIGHT AND MACALLUM. [Vol.1. 



appearance, ordinarily, which the contracted fibre gives is that 

 represented in Fig. 9, b. This mode of contraction seems to 

 find its closest analogy in the stalk of Vorticella. 



The Connective Tissues. 



Leuckart, in the first edition of his great work,^ described 

 two forms of connective tissue in Trematodes, the one forming 

 a granular reticulum with nuclei distributed through it, the 

 other composed of large vesicular cells which resemble the 

 cells of vegetable parenchyma. Both kinds of tissue are 

 also recognized by recent observers, the first being resolved 

 into a reticulum of branched cells, while the nature and func- 

 tion of the second have been variously interpreted. Looss,^ ^-g-t 

 speaks of them as remains of the original formative cells, 

 with a distinct nucleus surrounded by a thin layer of pro- 

 toplasm, which gradually gives out peripherically. Ziegler^ 

 attributes an osmotic function to them; but Schwarze 

 (pp. 58-71), who describes both their development and adult 

 structure in Distomum endolobum {^Cercaria armata), devotes 

 most attention to them. 



According to this author these vesicular cells are early 

 differentiated from the ordinary parenchyma cells, and soon 

 attain from twenty to thirty times the size of these. Their 

 plasma becomes hyaline and loses its staining capacity, 

 although an extremely fine granulation may be detected with 

 Hsematoxylin. Their function is to lend to the body that 

 liquidity which enables the cercaria to escape from the narrow 

 aperture of the sporocyst, but simultaneously, by virtue of the 

 pressure dependent on their own turgescence, to give to the 

 elastic investing membrane and the underlying musculature 

 that tenseness without which no movement is possible. They 

 may become altered in the adult through the assumption of 

 this osmotic function by other cells, notably those of the intes- 

 tine. 



We have studied these peculiar cells in Amphistoma sub- 

 clavatum, both in fresh specimens and examples prepared by 

 the method detailed above ; but we have found no cells in 



' Die menschl. Parasiten, p. 457. 



* Loc. cit., p. 398. 



3Zeit. wiss. Z06I., XXXIX., p. 550. 



