258 GENERAL HISTOEY OF THE INFUSORIA. 



The most striking points of divergence are the more definite and constant 

 figure of Act'inopliryina, their peculiarly formed tentacula in lieu of ordinary- 

 variable processes, and, of minor moment, their greater immobility, and the 

 operation of the tentacles in the introduction of food. Acineta was placed by 

 Ehrenberg with Actinophrys in a family or order Acinetina ; and most writers 

 treat them as if the relation between these two families were actually so near. 

 A closer attention will, however, prove that something more than a generic 

 diiference subsists, and that Acineta had better stand as the representative of 

 another group, well named Acinetina, although more limited in its significa- 

 tion than that so termed by Ehrenberg. The most tangible diff'erences 

 between Actinophryina and Acinetina are, that no food enters the substance 

 of the body in the latter group, and that the body is covered with an integu- 

 ment. The history of this division, as far as at present known, reveals yet 

 other distinctions ; for self- division has never been observed, whilst the pro- 

 duction of motile ciliated embryos from the interior has been seen over and 

 over again, without, as far as is known, an antecedent act of conjugation. It 

 must likewise not be forgotten, that it is the Acinetina which, according to 

 Stein's hypothesis, constitute an intermediate phase of existence in the de- 

 velopment of many Vorticellina. Indeed, could this naturahst's supposition 

 be proved, the existence of Acinetina as a class of independent beings would 

 at once be sacrificed. Another afiinity is discoverable with the Polycystina, 

 both in the natiu-e of the soft, muco- gelatinous mass, in the long, tentacular 

 filaments, and in the ciuTcnts of granules detected in the processes. This 

 relation is best seen with some Acanthometra {vide Midler's paper, Monats- 

 hericlit, Berlin, April 1855). The Actinophryina are related to the Ciliata also 

 by their sarcode, by the structiu'e and action of the contractile vesicle, b}" the 

 formation of alimentaiy vacuoles, and by the nature and composition of their 

 granules. But, over and above these general resemblances, a more special 

 afiinity is manifested if Cienkowsky's statement, that the fission produced is 

 clothed with vibratile cilia, be correct. This degree of affinity must be ad- 

 mitted in the case of the Acinetina which appear, as a rule, to generate 

 cihated embryos. 



Since the above history was written. Dr. StrethiU Wright, of Edinburgh, 

 has most kindly furnished us with notes on several Infusoria, among others 

 of two new forms of Actinophryina, presenting great peculiarities in struc- 

 tui^e. The accoimt of these novel genera wiU be found in the second part of 

 this work, in the Systematic History of the ActinopJiryina. 



SUBFAMILY ACINETINA. 

 (Plates XXIII. 1-23; XXYI. 3, 4; XXX. 3, 4, 7, 8, 21-26.) 



The reasons for separating Acinetina from Actinophryina, with which they 

 have generally been united, have been stated in the last chapter, where 

 likewise the difierential characters of the two groups, and the supposed part 

 they play in the cycle of development of Vorticellina, have been examined. 

 There remains therefore, to fill up the history of the Acinetina, nothing more 

 than some further remarks on the various forms they assume, and on certain 

 peculiarities in their structiu-e. 



The form of Acinetoi is subject to great variety. Ppiform and ovoid shapes 

 are the most prevalent ; but some are almost spherical, and others, again, 

 nearly triangular (XXIII. 6, 7, 8, 15, 17, 22, 23). A lobulated anterior end 

 is common ; and then the tentacles are usually restricted to the lobules (6, 17, 

 18). These lobed forms have no such firm integument or capsule at aU as 



