486 ORDER HOLOTRICHA. 



entire length of the body from the anterior and posterior extremities ; 

 endoplast ovate, subcentral ; trichocysts numerously developed, forming an 

 even, vertically disposed, subcuticular layer; natation vigorous, rotatory. 

 Length of body 1-120" to 1-96". 



HAB. Pond water and in vegetable infusions. 



This type, commonly known as the "Slipper Animalcule," is one of the 

 earliest observed and most widely distributed members of its class. It occurs in 

 countless numbers in artificial vegetable infusions, as also in its natural condition in 

 stagnant marsh and pond water. Viewed by transmitted light the dominant colour 

 is golden-brown, while by direct reflection it presents an almost opaline appearance ; 

 this circumstance, combined with the elongate contour of the animalcules, won for 

 them from Joblot and other earlier writers the popular name of " gold and silver 

 little fishes." The stellate contour of the two contractile vesicles at diastole, 

 referred to by most authorities as an essential characteristic of this species, 

 scarcely appears to belong to the natural or persistent state, but would seem to be the 

 result merely of artificial and abnormal pressure. The examination by the author of 

 numberless examples with the highest magnifying power, confined in space sufficient 

 to allow of their free movement, has failed to elicit in connection with these 

 structures otherwise than a perfectly even, spheroidal outline. Under those artificial 

 conditions in which the assumption of a stellate contour has been observed, the 

 contractile vesicles exhibit phenomena agreeing with those recorded later on of 

 Trachdophyllum apiculatum, Enchdyodon farctus, and other types ; minute, lateral, 

 pyriform sinuses make their appearance round the periphery of each vesicle at the 

 time of full diastole and, according to Carter, extend as thread-like canals through the 

 substance of the parenchyma. With the act of systole, the central spheroidal portion 

 of the vesicle disappears, leaving the stelliform peripheral sinuses, which now flow 

 together and form the next central vesicular dilatation. During the process of 

 transverse fission, as observed by Claparede and Lachmann, two new contractile 

 vesicles make then: appearance in advance of or anterior to the two old ones, these 

 latter, on the accomplishment of the act, occupying in each instance the posterior 

 region of the two newly developed zooids. The phenomenon of so-called longitudinal 

 fission, PI. XXVI. Fig. 30, accredited to this type by Ehrenberg, is now demon- 

 strated, as in the succeeding species, to indicate the act of conjugation between two 

 independent animalcules. The trichocyst layer in Paramcedum aurelia is very 

 distinctly developed, taking the form of an even series of minute rod-like bodies 

 disposed vertically immediately beneath the surface of the cuticle. An interesting 

 account of the earliest record of the existence of these structures, with the descrip- 

 tion of a simple process by which the animalcule may be induced to extrude them, 

 as communicated by Sir John Ellis to the ' Philosophical Transactions ' for the 

 year 1769, will be found at pages 81 and 82 of the preceding volume. 



The Paramcedum caudatum of Ehrenberg, distinguished by its more attenuate 

 posterior extremity, is regarded by Claparede and Lachmann as a mere variety of 

 this species, if not, indeed, exemplifying its most characteristic form. Paramcedum 

 aurelia, as figured by these last-named authorities, is represented as possessing a 

 conspicuous brush-like tuft of longer cilia at the posterior extremity. The author 

 has recently met with examples having this posterior brush-like tuft, and is inclined 

 to regard the same as signalizing a well-marked local modification, but certainly 

 not the predominant type of this cosmopolitan species. 



Paramaecium bursaria, Ehr. sp. PL. XXVI., FIGS. 31 AND 32. 



Body pouch-shaped, depressed, little more than twice as long as broad; 

 rounded posteriorly, narrowest and obliquely truncate at the anterior 

 extremity ; buccal fossa infundibulate, very wide anteriorly, extending 

 obliquely backwards from left to right to beyond the centre of the body ; 



