40 CLASS I. 



form of the body and of the short digitiform elongations, by means 

 of which they move : others again have filiform, branching append- 

 ages, that can be drawn in and out. There is no doubt that these 

 motions are to be ascribed to an internal power : they have alto- 

 gether the character of volition, for the creatures sometimes retard 

 their motions, or suddenly stop and again as suddenly swim quickly 

 away. Infusories make no distinction of day and night : they are 

 incessantly in motion, and no indication of sleep can be detected 1 . 



Coloured (red) spots have been supposed to be eyes, without 

 any particular proof: but neither a nervous system nor any distinct 

 organ of sense is to be found. 



The multiplication of these animals is by spontaneous fission of 

 the body, generally in the direction of the length. In this way 

 they can increase incredibly in a short time. In a very few multi- 

 plication by buds has also been observed 2 . 



1 EHRENBERG, Die Infiisionstkierchen, s. 529. 



2 Ex. gr. in Vorticetta (early observed by SPALLANZANI), see EHRENB. op. cit. Tab. 

 XXV. fig. ill. 2 ; in Epistylis, &c. 



[Besides the multiplication of infusories by longitudinal and transverse fission, and 

 that by external gems, other modes have been brought to light by the labours of COHN 

 and STEIN. They are forms of the encyst ing -process, which STEIN sees reason to believe 

 to be common to all true infusories. Colpoda cucullus does not undergo fission, but 

 becomes enclosed in a cyst, which in all cases is the secretion of the animal's surface. 

 Within this it multiplies by successive division, so that a progeny usually four in 

 number, occasionally eight, arises. Each of these is a special cyst, with its own 

 external membrane. The original cyst bursts, and the special cysts repeat the same 

 process, often several times, until at length the content of each special cyst escapes 

 through the ruptured external membrane as young Colpodce. STEIN, op. cit. pp. 15 

 25. Tab. in. fig. i 31. 



In Vorticettines (besides the generation by buds or germs, and by longitudinal fission), 

 the animal, becoming encysted, is changed into a spherical mass, in which none of the 

 original organs can be perceived except the ribbon-shaped nucleus, and a clear space, 

 which, however, does not pulsate. Processes are sent through the thin covering at the 

 upper exremity, and the form becomes some one of EHRENBERG's.4cwe&5, according to 

 the different genera, as Podophrya or Actinophrys. The nucleus, or rather part of it, 

 is then transformed into an internal embryo that rotates actively, and closely resembles 

 the germ-progeny of a young Vorticelline of the same species. This process is frequently 

 repeated in the same Acineta. The progeny may either encyst itself anew, and go 

 through the same process, or may at once secrete a pedicle, and become an ordinary 

 Vorticelline of the species. 



Such is the process in a young Vorticelline. In a full-grown large one it is different. 

 Here the encysted body is transformed into a homogeneous mass, the nucleus falls down 

 into a number (more than thirty) of disci-form bodies, which derive nutriment from a 

 portion of the liquefied substance of the mother-cyst : another portion of the maternal 



