268 GENERAL HISTOKY OF THE INFTJSOfilA. 



to disprove the origin of the alimentary globules in the Ciliata generally by 

 the introduction of liquid from without ; but it is to be remembered that in 

 these two groups of organisms we have very different structural conditions, 

 and that in the CiKata the entrance of water mostly holding solid particles 

 in suspension, through the oesophagus, and the moulding of it into a more 

 or less spherical outline, are matters sufficiently proved by direct observation. 

 We have stated above, that the vesicles are not contractile ; Dujardin has, 

 however, described those of Leucophrys striata as irregularly so. 



The cilia are disposed in longitudinal lines, and in some instances, where 

 there are ridges or margins, present a greater length and thickness, as, for 

 instance, upon the edges of the ciu'ved surface by which the 0. Planariai'um 

 adheres. 



The suiface can throw itself into plaits or folds, — an occurrence, however, 

 probably limited to animals in a diseased or dying state, as Perty remarks in 

 speaking of Opal'ina Eanarum (op. cit. p. 156). 



The Opalincea are not very active ; they swim onwards, moving at the same 

 time in an oscillating manner. 



The above account comprises all that can be stated of the Opalincea gene- 

 rally, since the differences in internal structure among the several reputed 

 species are so great, that it constitutes, as Stein points out {op. cit. p. 182), 

 a strong argument against the existence of the family as a group of inde- 

 pendent beings. However, from the study of the peculiarities of the several 

 members of the admitted genus Opalina, this author reduces them to three 

 types, viz. : — 1. The most common form of Opalina, represented by the 

 Leucophrijs striata of Dujardin, has an oblong body, marked by some 35 longi- 

 tudinal granular striae, and contains a number of vacuoles var}ing according 

 to external conditions, and a central band-Hke nucleus. This animalcule 

 occurs in the interior of the common earth-worm (Lmnbriciis). Stein found 

 them of different lengths from 1-60'" to 1-14'", and in all stages of the 

 process of transverse fission. "WTien placed in water, they become more active. 

 2. The second form differs from the preceding by the in-egular distension of 

 the body when placed in water : a strong endosmotic cuiTents sets in through 

 the enclosing waU and raises it from its contents, so that these at length pro- 

 duce the appearance of a smaller Opalina enclosed within a large one. Du- 

 jardin has described this variety under the name of LeucopTirys nodulata. 

 This Stein would imite with the first named, under the term of Opalina Lum- 

 brici, which, indeed, Schultze applied to the same animalcule. 3. The third 

 modification of Opalina might be treated as an independent species ; for, 

 notwithstanding a general resemblance, it has a striking pecuharity of its 

 own, visible under a strong magnifying power (such as 100 diameters), in the 

 shape of a single, strong, homy apparatus, placed near the anterior end on 

 the flat abdominal surface of the animal (XXII. 47). From a short common 

 base situated to the right of the median line, slightly cui^ed, uncinate, 

 pointed processes are given off, of which one is much longer and stronger 

 than the other. To the left of this organ a fold or furrow occurs in the 

 surface, which might be mistaken for the entrance to a mouth. The deve- 

 lopment of this organ may be readily followed during self- division. It 

 appears first as a homy protuberance close to the line of section (XXII. 47), 

 which extends backwards into the base of the process, and forwards or up- 

 wards into the two hooks. It is also worthy of notice, that generally a greater 

 or less number of solid oval nucleoli and short rod-like bodies make theii' 

 appearance within the homogeneous substance of the nucleus. The Opalina 

 Lumhrici of Dujardin is no other than the animalcule described, although its 

 characters are incoiTectly represented by that author, who, from his figure, 



