258 BALANTIDIUM COLI. 



tremity. But even the more slender specimens exhibit on the whole 

 but slight contractility, and are never specially lively. The most 

 striking movement one sees is that of the peristome and anterior end 

 of the body, which sometimes stretches out like a neck/ and bends 

 round towards the somewhat less convex ventral surface. 



This is correlated with the nature of the body, which has its inner 

 parenchymatous substance packed full of food, leaving only the front 

 part of the body unoccupied, and reducing the cortical layer to a com- 

 paratively thin sheath. It is, however, well defined, since the two 

 masses differ widely in nature and appearance, and are sharply dis- 

 tinguished from one another. 



TJie Interior Mass consists of a substance finely granular through- 

 out, in which one can distinguish fat granules of varying size, and, 

 especially in the posterior half, one or two larger granular bodies 

 (faecal masses?). Occasionally, too, one sees a starch granule, 

 especially when the pigs are feeding copiously on potatoes. Wising 

 has also observed red and white blood corpuscles (pus corpuscles ?) in 

 the interior of the Balantidia infesting the human intestine. Since, 

 on the whole, but few firm and definite bodies are found in these 

 animals, we may perhaps conclude that their food consists mostly (as 

 in the other species of Balantidiwn) of the more pulpy contents of 

 the intestine. In contrast to the thick interior substance, the cortical 

 layer consists of a clear, almost transparent, protoplasm, exhibiting that 

 striated appearance which often occurs, and more conspicuously than 

 in the present case, among the Infusoria. The striae all start from the 

 peristomial region, and run in long spiral lines to the posterior ex- 

 tremity. They are most distinct in front, and in their arrangement 

 present an almost radiate appearance. They consist probably of fine 

 fibres, which are embedded in the cortical layer at equal distances 

 from one another, and which squeeze the looser parenchyma between 

 them into frills. At the anterior end of the body one can often see 

 these frills in profile as little marginal knobs. On its surface the 

 cortical layer bears a somewhat firm cuticle with cilia, which are, as 

 Malmsten pointed out, more thickly arranged between the above- 

 mentioned frills. 



Observers are not altogether consistent in their descriptions and 

 representations of the peristome. Previously to Stein's researches it 

 was usually regarded as the mouth opening, and is so still by some 

 (Ekeckrantz). This idea is tenable so long as one examines it only 

 in its short and rudimentary state, but not when one compares it with 

 the more developed peristome of other species. This comparison 

 leaves hardly any doubt as to the fact that this structure forms part 

 of the outer body-wall, a part, moreover, easily distinguishable from 



