GENUS CHILODON. ^a^ 



fusiform, median, with a distinct centrally enclosed endoplastule ; contractile 

 vesicles many in number, irregularly distributed. Length of body 1-250" 

 to 1-84". Hab. — Salt and fresh water. 



This species represents one of the commonest infusorial forms, it abounding in 

 both fresh and salt water and in stagnant infusions. Since under different conditions 

 it presents a variety of aspects, it has, as might be anticipated, received at the 

 hands of independent observers a multiplicity of titles. Among the numerous 

 synonyms that Stein has thus found it necessary to divest this species of in his 

 admirable monograph of the Hypotricha, the following may be mentioned : — Colpoda 

 cuaillulus and C. cucidio of O. F. Miiller, Loxodcs cticiillulus and Chilodoti imcinatus 

 of Ehrenberg, Loxodes ciiciillulus, L. cucidio, and L. dcntatus of Dujardin, and Chilodon 

 uncinatiis, Loxodes cucuUidus, L. cucidio and Z, brevis, and Chilodon uncinatus of Max 

 Perty. All of these so-called species are now shown to be mere transitional growths 

 or imperfectly observed examples of one and the same type, and for which the 

 distinctive title of Chilodon cucidlulus, as first applied to it by Ehrenberg, must 

 be retained. A large number of the synonyms above quoted would seem to have 

 arisen from the observation and description of the animalcule in its immature state 

 and at which period, as shown by Stein, its aspect differs considerably from that 

 of the adult form. Thus while in its mature condition the animalcule, throuo-h 

 the greater induration of its dorsal cuticular surface, is tolerably rigid and constant 

 in form, this does not apply to the species when first released from the eo-o- or 

 spore, or when liberated from their characteristic capsular encystments. Under 

 these conditions the entire body is completely soft and plastic, the anterior 

 extremity is more rounded, and the general appearance of the animalcule more 

 nearly approximates that of the Holotrichous genus Colpoda. Multiplication by 

 both transverse and longitudinal fission is common in this species, the last named 

 process, according to Stein, being likely to be mistaken for the phenomenon of con- 

 jugation. The characteristic oral or pharyngeal rod-fascicle makes its appearance at 

 a very early stage, before indeed the appearance of the cilia or its extrusion from 

 the sporocyst, and is likewise developed in duplicate as a preliminary to the 

 process of longitudinal or transverse fission. Examples of this species were 

 recently obtained by the author in vast quantities from a small road-side gutter near 

 St. Heliers, Jersey. Every individual almost was found to be gorged with small 

 Navicidce. and other minute Diatomacec^e, which constitute a favourite diet of this 

 animalcule. Examined with a power of about 700 linear, the disposition of the 

 ventral cilia in fine parallel lines was clearly shown, as also that the cilia upon these 

 hnes work in an opposite direction on each side, finally converging at the oblique 

 anterior linear groove, and conducting the current of water down this channel to 

 the mouth. Stein represents this groove as a simple oblique line clothed with a 

 differentiated and more closely approximated fringe of cilia. In specimens killed by 

 the application of osmic acid it was clearly demonstrated, however, that this Ime is 

 not specially ciliated, but forms a narrow gutter-like channel for the conduct of 

 food-particles to the oral aperture. The elongate ovate endoplast with its enclosed 

 endoplastule was very distinctly exhibited in the majority of examples examined. 



The author is indebted to Mr. Charles Stewart, of St. Thomas's Hospital, for 

 the opportunity of examining preserved examples of Chilodon cucidlulus that are 

 distinguished by a highly interesdng development of the elements entering into the 

 composition of the pharyngeal armature. In place of contributing towards the 

 formation of a symmetrical subcylindrical tubular fascicle, as usually obtains, the 

 inferior or proximal denticles more especially are developed backwards to a 

 remarkable extent and recurved upon themselves in the manner illustrated in 

 PI. XLII. Fig. 20. The general effect produced is suggestive to some extent of the 

 not infrequent development of a rodent's incisor teeth, as brought about through 

 the loss or injury of the opposing set, and which under ordinary conditions restrain 

 their growth beyond the normal limit. 



