OF THE EOTATOKIA. 393 



out an enveloping tube, adhere to foreign substances by the tip of the foot, 

 and elevate the body in an erect position), the dorsal aspect is always deter- 

 minable by the eye or eyes being towards that sui^face, by the stomach and 

 intestine passing do^vn it, and by the cloaca being on that side of the foot. 

 The ventral aspect has the manducatory apparatus and the ovary." 



But, besides these great divisions, all the Eotifera exhibit transverse lines, 

 folds, or joints, analogous to those seen in the Articulata, especially among 

 the Cnistacea, such as the lobster and shrimp. Mostly, such are but folds or 

 wiinldes, and not true articulations, in the Rotatoria (though perhaps as much 

 so as the like in the larvae of many insects), and consequently disappear on 

 the extension of the animals. However, in not a few instances, veritable 

 articulations occm% — e. g. Hydatina, Rotifer, Eosjpliora, PhUocUna (XXXYIII. 

 1, 2). In Eiwhlanis dilatata, writes Ehrenberg, the abdominal surface pre- 

 sents four decided articulations. The minimum development of the articulate 

 condition occurs in those genera the most removed from the liotatorial type, 

 viz. in Stej^hanoceros (XXXVII. 1), Lacimdaria (XXXVII. 19), and some 

 anomalous Notommata (XXXVIII. 28), which only present fine lines under 

 the surface, looking like annular threads. The construction of the joints is 

 peculiar, one portion or segment sliding within another after the manner of 

 the tubes of a telescope. This telescopic action is best illustrated in the 

 genus Philodina, where the entii^e body is fusiform and articulated ; but it is 

 oftentimes to be seen also in the tail-process, when absent or imperfect in 

 the rest of the body, — e. g. Brachioniis, Noteus (XXXVIII. 25), StepTianops 

 (XL. 8-10), Scaridkmi (XXXVIII. 22). An incomplete articulation, or 

 mere wrinkling, is seen in the pedicle of Megcdotroclia, Melicei^ta, and Lacinu- 

 lana (XXXVII. 17-19). 



AH the Rotatoria are invested by a fii-m, usually smooth and elastic, 

 integument or skin, which follows the contained parenchpna in all its con- 

 tractions, accommodating itself to the various movements of the body. It is 

 more delicate on the head, where the cilia are inserted, and there becomes 

 continuous ^\ith the membrane of the interior. It is composed of two layers 

 — an external, the cuticle, and an inner, immediately subjacent, the dermis 

 (XXXVIII. 2Q). 'WTiere the structiu'e is not evident, it may be rendered so 

 by the use of chromic acid. The cuticle is homogeneous, structureless, and 

 firmer than the dermis, which is soft, granular, and contains in its thickness 

 numerous fat-globules and nucleated particles (XXXVII. 29). The latter 

 tissue acts as a lining to the general cavity of the body, and gives attachment 

 to the muscular cords of the interior. It is much developed about the head, 

 beneath the vibratile ciliaiy apparatus, and there sends inwards numerous 

 projections or lobes (XL. 2), which Ehrenberg assimied to be of a muscular 

 nature, and to be permeated by vessels and nerves. At other parts also, 

 dehcate fibres or threads are seen to pass inwards from the dermis to the 

 \iscera, sustaining and connecting them together. These fibres have some- 

 times been described as muscles, at other times as nerves. The former is 

 apparently their true nature, although, as Cohn believes, nerve-fibres may be 

 mixed among them. 



The integument is histologically, i. e. in its anatomical nature, a connective 

 tissue derived from the coalescence of branching cells, and still presents in 

 its inner layer the scattered nuclei of the original cells, in the form of the 

 nucleated particles described. Where the dermis is much developed, its soft 

 tissue becomes here and there hollowed out into clear spaces or vacuoles, 

 which have been mistaken for nerve -ganglions, especially when situated in 

 the head (XXXVII. 29). 8o, again, at the posterior part of the body, 

 behind the viscera, and in its prolongation or foot-process, where the dermic 



