Mr. H. J. Carter on Ploesconia and Kerona. 249 



gill, we have features which agree so precisely with Ehrenberg^s 

 Oxytricha Pellionella, Kerona Polyporum, and Stylonychia Silurus, 

 as well as with the " Oxytricha" figured by M. J. Haime as the 

 larva of Trichoda Lynceus, that, with the variable appearances 

 assumed by Kerona pustulata in difiierent stages of develop- 

 ment, I am inclined to think that all these may be only different 

 forms of this species, — an inference which meets with no op- 

 position from Ehrenberg's delineations, since these and his 

 figures of the Ploesconice are the most unsatisfactory of all his 

 representations. Even his Oxytricha caudata has the moveable 

 legs in front, which make it a Kerona ; at least there is a form 

 here exactly like it in general contour, which is undoubtedly a 

 Kerona in this respect. Dujardin^s delineations of these ani- 

 malcules are not a bit better : the want of care, labour, and con- 

 sequent preciseness with which they have all (his as well as 

 Ehrenberg^s) been drawn, renders their details so doubtful, that 

 they are worse than useless for identification. Vexing as this 

 is, however, it should not be forgotten that the subject is one 

 which is attended with the difficulties mentioned at the com- 

 mencement of this paper. 



Multiplication by longitudinal and transverse division, as well 

 as by budding, are all equally common in Kerona pustulata ; 

 and here also the longitudinal division is very likely to be mis- 

 taken for copulation, from the inferiority in size of the left indi- 

 vidual, particularly if there are not sufficient examples present 

 to show this in all its stages. 



General Observations, 



On comparing Ploesconia with Kerona, we cannot help seeing 

 the unity of plan on which they are constructed, while the dif- 

 ferences in the consistence of the body, definition of form, 

 development of the posterior legs, situations of the contracting 

 vesicle and anal orifice respectively, form and position of the 

 nucleus, and the presence of cilia round the margins in Kerona, 

 are quite sufficient to make them separate families. 



Again, we cannot help remarking in the inferior family, viz. 

 Kerona, the downward approach towards Paramecium Aurelia, 

 in the resistant state of the body, the ciliated margins, and the 

 position of the anal orifice, which is exactly the same as that in 

 Paramecium, while it is the opposite to that of Ploesconia, 



Then, in the other genera of the Kerona, such as Oxytricha, 

 we have not only the posterior but also the anterior legs motion- 

 less and styliform, which is a still nearer approach to Para- 

 mecium, in which such appendages are altogether absent. 



As regards the approach of the Ploesconia to higher Inverte- 

 brata, we have certainly legs, which apparently move on short 



