1880.] 



MICROSCOPICAL JOURNAL. 



69 



what denser outer layer, and a 

 transparent, structureless mem- 

 brane, or cuticula. In many spe- 

 cies the three layers are readily dis- 

 tinguished, in others they pass im- 

 perceptibly from one to another. 

 The parenchyma is capable of con- 

 traction and expansion. Many spe- 

 cies can only bend and curve them- 

 selves to a slight extent, and their 

 shape is, therefore, quite definite ; 

 others can stretch out or contract, 

 bend and writhe the entire body, 

 and their forms are constantly 

 changing — metabolic. Externally, 

 the body is furnished either with 

 one or several whip-like appen- 

 dages — flagella, — or with suctorial 

 tubes, which are expanded at their 

 ends — tentacles, — or with cilia of 

 various lengths and sizes, which 

 may completely cover tlie body or 

 be found only on certain parts of it. 

 Hence, the class of Infusoria is 

 divided into three orders : 



FlageUata (Flagellifera). 



Acinetina (Suctoria, CI. and L.). 



CiKata. 

 Only the Ciliata are positively 

 known to be provided with a 

 mouth. Whether the FlageUata 

 possess a mouth is not certainly 

 known. All have, however, in the 

 outer parenchyma, near the surface, 

 at least one contractile vesicle. If, 

 as is usually the case, only one ves- 

 icle is present, it generally lies near 

 the posterior end of the body. Many 

 species have several vesicles, the 

 number and position of which are 

 generally constant. In the vesicles 

 a watery fluid periodically collects 

 from the body-mass, and from time 

 to time is suddenly emptied, a por- 

 tion always passing out through an 

 ever-present opening in the paren- 

 chyma. 



The outer parenchyma of all In- 

 fusoria contains at least one nucleus, 

 often more of them, and in many, 

 (not all) near the nucleus, or in a 



cavity of it, is a smaller nucleolus. 

 Both are sharply defined, with a 

 structureless membrane and homo- 

 geneous, finely granular contents. 

 They are not always plainly visi- 

 ble, but become so by the action of 

 dilute acetic or chromic acid, or by 

 staining with carmine or red ani- 

 lin solutions, which color them 

 more intensely than the paren- 

 chyma. 



The ordinary process of multi- 

 plication is by simple cross-divi- 

 sion; longitudinal or oblique divi- 

 sion takes place only in a few. 

 What has been considered as lon- 

 gitudinal division is, in most cases, 

 the separation of two conjugating 

 individuals. Other processes of 

 multiplication — by budding, swarm- 

 scions or embryos (eggs ?) — are often 

 observed in single genera, but we 

 cannot yet regard these as general 

 phenomena. All of them are intro- 

 duced by the division of the nucleus, 

 or at least accompanied by it. Von 

 Siebold and after him Kolliker, 

 Clauss, Hackel and others, there- 

 fore, regard the nucleus in the In- 

 fusoria as analogous to the cell-nu- 

 cleus of plants, indeed, the Infusoria 

 themselves as unicellular animals. 

 On the other side,especially by Stein, 

 these ideas are strongly opposed, 

 for the differentiation of the infuso- 

 rian body seems to be too much com- 

 plicated for a simple cell ; it might 

 be regarded as a many-celled struc- 

 ture not resolvable by our optical 

 and chemical means, or else as a 

 fusion of different cell-combina- 

 tions. 



Still others reach the conclusion 

 that the ordinary conception of a 

 cell is not applicable to these low 

 organisms. 



Many, if not all Infusoria possess 

 the peculiar faculty of contracting 

 into balls under unfavorable con- 

 ditions of life, e. g., want of water, 

 and by the secretion of a firm, 



