0^ THE ROTATORIA. 419 



the walls of other portions of the alimentary canal, and is supposed by many 

 to contain muscular fibrilloe, although so very thin, pellucid, and apparently 

 structiu'eless. Ley dig, however, calls it a homogeneous connective tissue. 

 The lining of epithelium is made up of large turgid cells, rendering the wall 

 thick and of a pulpy appearance (XXXVIII. 26/). In young animals the 

 epitheUal cells are coloiu'less ; but in adult beings their granular contents 

 are coloured and interspersed with fat-globules, whence it is that the walls 

 of the stomachs assume a yellowish hue often intermingled with green and 

 broAvn tints. The cells, moreover, commonly possess a nucleus and a nucle- 

 olus, and their free surface is constantly ciliated. They are readily detached 

 from the subjacent membrane and from each other, and are then seen to have 

 a spherical or ovoid figui'e. 



" The great thickness of the epithelial layer," writes Mr. Williamson, ^' as 

 compared with the entire diameter of the organ, is curious : whilst the latter 

 averages about 2^1^^ ^^ ^^ inch, the former is often not less than y^th, 

 or -i-th of its entire diameter. The cells, when detached, vary in size, from 

 a diameter of ^^^^^ th to ^. ^}^ ^ th of an inch ; one of these was fringed with 

 ciha y^T^-jjth of an inch long, and had a nucleus y^J^th of an inch. After 

 being detached, some of the ciliated cells floated slowly away, like so many 

 animalcules." 



Although this description and the measurements refer specially to the 

 Melicerta rhigens, yet the relatively large size of the cells is a feature com- 

 mon to all the Rotatoria, and has been pointed out and figured by Leydig, 

 Siebold, and others. 



The second stomach, noticed by Williamson in Melicerta, also had a layer of 

 epithelial cells bearing cilia " even longer than those of the upper viscus, 

 — although the paiietes were very much thinner and more transparent, the 

 cells being less easily traced." In the third or lowest dilatation, seen by 

 Huxley in LacinuJaria, the interior was clothed with very long cilia (XL. 4). 



Ehrenberg remarked the existence of large stomach- cells in Diglena la- 

 custris, and of less distinct ones in Notommata Myrmeleo and N. Copeus. The 

 pouches he speaks of around the alimentary tube of Hydatina senta, and 

 which imparted the appearance, to Ms eye, of a bunch of grapes, are no other 

 than epithelial cells. In Philodincea the intestinal canal is stated to be fili- 

 form, and enveloped in a granular cellular mass ; that is to say, the calibre is 

 very much reduced by the tiu'gid cells lining the walls. The compact mass 

 of blind tubules, so described in Eotifer, admits a like interpretation. 



In Notommata tardigrada Leydig failed to detect cilia either in the stomach 

 or intestine. 



In the great majority of the Rotatoria a definite ^' intestine " follows the 

 stomach, and ends below in the cloaca. This intestine is generally known as 

 the " rectum,''^ and is supposed to represent the large intestine of higher ani- 

 mals. It varies much in its dimensions in different species, especially in its 

 length and course. It is long, straight, and capacious in Notommata centrura 

 (XXXYIII. 26), and in Euchlanis triquet7'a (XXJLYIII. 5), short in Lacinu- 

 laria, and extremely short in Notommata tardigrada. 



Among the encased Rotatoria it is of considerable length, owing to its 

 curving forwards from the second stomach, so as to reach its outlet near the 

 margin of the enclosing urceolus, or in other words the neck of the animal, 

 and thereby provide for the immediate removal of the excrementitious matter 

 from contiguity with it (XXXYII. 17). In Stephanoceros and Floscidaria, as 

 exceptions to this rule, this intestine is short. Looking at the so-caUed second 

 stomach, placed at the head of the rectum in these fixed Rotifers, we might 

 rather assimilate it to the caecum, wliich in some of the higher classes forms 



2e2 



