494 ORDER HOLOTRICHA. 



have remarked of the singular-shaped endoplast of this species that it is not, as in 

 most instances, imbedded within the cortical layer, but lies loosely in the semifluid 

 internal endoplasm, permitting the body to revolve freely over and around it. This 

 phenomenon of the revolution of the body over the endoplast has been reported 

 by Siebold in connection with other infusorial types, but has been explained by 

 Eckhard as being a mere optical illusion. Claparede and Lachmann are, however, 

 so thoroughly convinced of the free suspension of the endoplast in this instance, 

 that they are disposed to accept Siebold's statement as correct. It is a matter of 

 regret that the discoverers of this species have omitted to place on record both the 

 dimensions and habitat of this highly interesting type. Judging from the size of 

 three species of the same genus, Prorodon marinus, P. armatus, and P. griseus, 

 delineated in their treatise, it would appear to considerably exceed these in size 

 and to most nearly approach P. niveus. 



Doubtful Species. 



The Habrodon curvatus of Max Perty, ' Kleinster Lebensformen,' 1852, charac- 

 terized as follows, would appear to be rightly referable to the genus Prorodon : 

 " Body subcylindrical, slightly curved, thickened posteriorly, mostly truncate in front ; 

 oral aperture anterior, associated with a very delicate dental apparatus ; anal aperture 

 postero-terminal ; cilia disposed in longitudinal rows, colour grey or pale green ; 

 movements slow. Length 1-390" to 1-132". Hab. Spring water, with Chara, 

 Bern." 



GENUS II. NASSULA, Ehrenberg. 



Animalcules ovate, cylindrical, flexible but not polymorphic, usually 

 highly coloured ; oral aperture lateral ; pharynx armed with a simple horny 

 tube, or with a cylindrical fascicle of rod-like teeth ; entire surface of cuticle 

 finely and evenly ciliate ; the cortical layer sometimes containing tricho- 

 cysts ; contractile vesicle single or multiple. Inhabiting fresh water. 



A prominent characteristic of the genus Nassula is the normally bright colouring 

 of the parenchyma or body-contents rose-colour, red, green, blue, yellow, and 

 violet being separately developed or variously combined in the several species. 

 In that form, N. ornata, with which the colour violet is more usually dominant, 

 this pigment occurs distributed in scattered vesicular patches, which are most 

 abundant in the anterior region. Ehrenberg was led to regard these coloured 

 vesiculae as glands possessing probably a biliary function. By Stein, however, 

 both the generally dispersed and vesicular aggregations of colouring matter are 

 pronounced to be merely the product of incepted food-material; certain Oscilla- 

 toriae devoured by one variety, N. ambigua, having been observed by him to pass 

 successively through the tints of green, blue, and red during the process of digestion. 

 Claparede and Lachmann, while endorsing Stein's views so far as relates to the 

 coloured material within the semifluid endoplasm, and which is in a constant state 

 of circulation, are inclined to attribute to the stationary pigment-corpuscles imbedded 

 within the cortical layer the character of organs whose special function is not as 

 yet determined. Stein has recently proposed to separate Nassula ornata, JV. rubens, 

 and all other members of this generic group in which trichocysts are abundantly 

 developed, under the distinct title of Acidophorus. Such importance is not, how- 

 ever, here conceded to the presence of these structures, their development being 

 subject to considerable variations even among individuals of the same species. The 

 distinct lateral location of the oral aperture serves to readily distinguish this genus 

 from Prorodon. 



Nassula ornata, Ehr. PL. XXVI. FIG. 42. 



Body ovate, cylindrical, two or three times as long as broad, brownish- 

 green, variegated with violet vesicles ; pharyngeal rod-fascicle forming an 



