560 ORDER HOLOTRICHA. 



The reproductive phenomena, and origin of the primary encysted bodies, as 

 reported by Zeller, remain to be recorded. These, so far as it has been yet 

 ascertained, are brought about by a process of repeated binary fission of the 

 primary animalcule, agreeing in its earlier manifestations with that characteristic of 

 the majority of the members of the Infusorial sub-kingdom, but which in its later 

 phases follows a remarkably distinct plan. The subdivision of the adult zooids 

 of Opalina rauarum is accomplished in a twofold manner, partly by oblique 

 and partly by transverse fission. The first subdivision always takes an oblique 

 direction, PI. XXVI. Fig. 2, separating the animalcule into two halves, the fore- 

 most of which has a broader anterior and sharply-pointed posterior extremity, 

 communicating to it a close resemblance in contour to the ordinaiy zooids of Opalina 

 obtrigona, or to the half-grown examples of the present species, as already described. 

 The hinder half remains bluntly rounded posteriorly, and differs but slightly in 

 aspect from the adult form. The separated moieties continue multiplying by further 

 fission alternately in an oblique and transverse direction, until at length the divided 

 fragments do not exceed the i-yooth to i-55oth part of an inch in length. These, 

 as delineated at PI. XXVI. Fig. 5, have an evenly ovate outline, their move- 

 ments gradually grow more languid, and in a little while they contract into a sub- 

 spherical form, and secreting around them a transparent indurated membrane, 

 become metamorphosed into cyst-like bodies, resembling those out of which the 

 adult zooids had been observed to develop. The average diameter of these cysts 

 varies from 1-1250" to i-iooo", though occasionally larger ones measuring 1-625'' 

 Avere met with. The minutely di\-ided Opaliim were observed by Zeller at the 

 time of their encystment to enclose within their parenchyma a variable number of 

 the spheroidal endoplasts that characterize the parent zooid, though subsequent 

 to their encystment an important metamorphosis of these structural elements was 

 effected. So long as the spore-like cysts remained isolated in the outer water, 

 as voided with the excreta of the adult frogs, no modification in the character 

 or number of the contained endoplasts occurred, but on the cysts being devoured 

 by the young frog-larvae or tadpoles, these numerous endoplasts disappeared and 

 were replaced by a single larger spheroidal one. It was with such a single endo- 

 plast that the zooid usually broke its way from its cyst into the intestinal tract 

 of its new host, though occasionally the single endoplast did not take the place 

 of the more numerous minute ones until a little while after its exit from the 

 cyst. Whether the single larger endoplast is built up through the coalescence 

 of the several smaller elements, or whether these latter entirely disappear prior to 

 the appearance of the former, was not definitely ascertained, though the evidence 

 elicited most strongly supports the last alternative. The growth onward from the 

 minute newly released animalcule is but a recapitulation of the data already recorded. 

 In addition to the multiplication by fission productive of animalcules of gradually 

 diminished volume, and terminating in encystment, a simpler process of fission, 

 corresponding with that of the more ordinary Infusoria, and producing zooids which 

 grew again directly to the parent form, was found to take place later in the year, 

 including more especially the months of August and September. A more abnormal 

 elongate contour is not unfrequently presented by the animalcules of this species 

 when first emerging from the most minute cysts. Sometimes both these and the 

 smaller zooids resulting from the final phases of duplicative division, possess, as 

 shown at PI. XXVI. Fig. 9, an altogether ragged outline, indicative of the soft and 

 glutinous consistence of the ectoplastic element. 



In living examples of Opalina ranaruin recently examined by the author when 

 dissecting frogs at the South Kensington Laboratory, it was observed that the 

 movements of the cilia during the progress of the animalcules over the smooth 

 surface of the glass object-carrier, exhibited a very singular aspect — vibrating rhyth- 

 mically in more or less even, parallel, wave-like series, and temporarily conveying 

 the appearance, as shown at PI. XXXII. Fig. 19, of their disposition in such order 

 upon the surface of the cuticle. 



