396 GENERAL HISTORY OF THE INFUSORIA. 



In the last-named genus they attain a still more complex natiu-e, and assume 

 a plumose (feather-like) structui^e (XXXYIII. 30). 



The opposite condition is seen in depressions or pits, few and scattered, on 

 the surface of the integument, often apparently surroimded by a margin. 

 Illustrations are found on the dorsum of Polyarthra, of Notommata Myrmeleo, 

 and of N. Sieboldii (XXXYII. 32). 



All the markings and processes of the integument of Rotatoria are produc- 

 tions of the chitinous cuticle, just as hairs, feathers, horns, and claws in the 

 Yertebrata originate from the epidermis. They are similarly affected by 

 chemical reagents, and decompose mth the same facility as the integument 

 which supports them. They are, moreover, of much value in supplying 

 generic and specific characters. 



Several genera possess, in addition to the integument immediately investing 

 them, an external sheath oi' case, to the bottom of which they are attached 

 by a prolongation of the body in the form of a contractile pedicle. This 

 external sheath received from Ehrenberg the particular designation of 

 ' urceolus ; ' and consequently the beings inhabiting it were said to be uix-eo- 

 lated, or, as many prefer to say, are ' encased.' The composition of the case 

 varies greatly ; for, although it originates always as a secretion from the 

 animal itseK, the substance differs in different genera, both in its characters 

 and modes of formation : moreover, in some species, particles of foreign 

 matters are superadded, to give it strength and solidity. 



The cases of Floscularia (woodcut, Part II.) and Stephanoceros (XXXYII. 

 1) are coloui4ess, and apparently structureless, and, though roomy, are visible 

 with difficulty on account of their tenuity and transparency. They are best 

 demonstrated by the addition of some colouiing matter, such as indigo, to 

 the water in which they are examined. An exception to the usually trans- 

 parent homogeneous case of Floscularia occurs, according to Dr. Dobie, in F. 

 campanulata. Dujardin, again, asserts that the uixeolus of Flosculana may 

 vanish dming the lifetime of the animal, and that in many French species 

 it is always absent ; he therefore denies its value in generic distinctions. 

 His statements, however, require confirmation, being opposed to the observa- 

 tions of other naturalists. 



Again, the tubes of CEcistes, ConocJiilus, and Lacinularia are hyaline, with 

 a more gelatinous consistence, and, in the two last genera, adhere together. 

 In ConocMlus the individuals are aggregated around a central globule of 

 gelatine, from which they project like so many rays ; whilst in CEcistes each 

 luxeolus is free, but has its surface encrusted mth foreign particles. Tuhi- 

 colaria (XXXII. 379) has a thick gelatinous case, of a milky hue, which, 

 from its effervescing on the addition of an acid, is attributed to a deposit of 

 carbonate of lime within it. In young animals the case is quite transparent. 

 This is also true of the urceolus of Limnias (XXXYI. 2), which, as it grows 

 older, changes to a brown and brownish-black colour; and, as it is viscid, 

 various extraneous bodies affix themselves to it. In one newly- discovered 

 species, the usually smooth surface is departed from, and the case becomes 

 annulated, and is also semitransparent. Dr. Bailey found in North America 

 a species of Melicerta mth a brown annulated urceolus. But the most re- 

 markable tubular sheath is that of Melicerta ringens (XXXII. 386 ; XXXYI. 

 1), which is composed of equal-sized lenticular peUets, of a brownish- red 

 colour, and of a substance secreted by the animal itself and deposited in a 

 regular oblique or spiral series. This wonderful phenomenon wiU be consi- 

 dered hereafter, in the section on Secretion. The cohesion of particles of 

 foreign substances to the enclosing tubes is seen also in some Annelida, and 

 in the aquatic larvae of certain Insects. 



