210 On the Structure and Natural History of the Vorticellfe. 



Besides the longitudinal fibres, we find in the ciliated disk 

 and in the peristome circular fibres ; but in these parts, also, I 

 have been unable to make out whether they have a spiral 

 course corresponding with that of the ciliary spiral. 



To the skin and the above-described muscles a protoplasmic 

 zone adheres within on all sides — the true cortical layer of the 

 Infusorian body, which encloses and lines the whole internal 

 space or hody-cavity , upon the nature and signification of 

 which we shall shortly go into detail. If a Vorticellan be 

 slowly compressed under the glass cover, by abstraction of 

 water we see, especially at the moment of its death, a distinct 

 vesicular and often almost regularly polygonal marking 

 [Epistylis Jlavicans) make its appearance beneath the skin. 

 This belongs to the above-mentioned cortical layer of the 

 body. Whether this vesicular arrangement of the protoplasm 

 exists during life, or only makes its appearance after death, I 

 have been unable to ascertain positively. In this cortical 

 layer, and held by it in their position, are seated the principal 

 organs of the taody, namely the nucleus, the contractile 

 vesicle, and the principal section of the alimentary canal, 

 which we shall also consider more particularly hereafter. 



Finally, I must here refer to the exceedingly peculiar 

 structures situated beneath the skin, of which a passing 

 mention has already been made, with the indication that they 

 ought possibly to be regarded as urticating organs. I have 

 hitherto found these organs only in Epistylis jlavicans, and 

 even here not constantly; in connexion with which, however, 

 it must be remarked that very probably several species, or at 

 any rate varieties, have hitherto been included under the above 

 name. The bodies in question are oval or pyriform, sharply 

 contoured, shining capsules, which almost always lie together 

 in pairs, and apparently in the cortical layer (PI. XV. figs. 

 6 k, 7, & 8). They are of great firmness, and present great 

 resistance to caustic potash and the like ; but if they are 

 removed from the body and compressed, a tolerably long and 

 powerful thread springs forth from each of the capsxdes 

 (PI. XV. figs. 7 & 8 ^), and generally from the somewhat 

 pointed end, which, in the above comparison, represents the 

 stalk-end of the pear. The expelled thread usually forms 

 several convolutions and loops, is motionless, and shows 

 no special structural characters ; by careful examination 

 it may also be seen rolled up, apparently in a spiral, in 

 the interior of the still closed capsule (PI. XV. fig. 7 a). 

 What is the interpretation of these structures ? Are they 

 proper to the Vorticellan body and formed in it ? or are they 

 foreign organisms which have penetrated into it? In the 



