ZOOLOGY AND BOTANY, MICEOSCOPY, ETC. 905 



the presence of a firm shell, and it offers yet another proof of how 

 easily division may pass into gemmation. In Acineta mijstacina he 

 has observed that gemmation, fission, and the separation of small 

 pieces may all be observed at the same time ; this deviation from the 

 mode of simple fission, which is the primitive and fundamental mode 

 of reproduction among the Protozoa, is clearly due to the need of 

 rapidly producing a large number of individuals ; but it is just as 

 clear that the sole mode of reproduction among the Thalamophora is 

 a mode which follows the type of the division of the cell. 



The statements of the author in regard to the striation of the 

 flagella and similar points of minute anatomy must be received with 

 great caution, to say the least. 



Structure of Trichodina steinii.* — F. Vejdovsky identifies the 

 Infusorian described without name by Hallez in his recent work on 

 the Turbellaria, p. 84, pi. v., figs. 22-5, with the species Trichodina 

 mitra, and proceeds to rectify sundry errors in that author's descrip- 

 tion and some omissions in the account given by Claparede and 

 Lachmann from the study of the species, T. steinii, described by those 

 authors and found on Planaria gonocephala. The oral circlet of cilia 

 runs round the anterior end of the body, beginning and ending in the 

 mouth-opening ; it is accompanied by a fine undulating membrane 

 which lies at its inner side and in contraction serves to close in the 

 mouth-opening. The organ of fixation is a hollow, fimnel-shaped 

 structure, possessing, in contrast to the complicated arrangement in 

 T. pediculus, only a set of simple hooks on the outer side ; the edge is 

 lined by long, closely-set cilia, not by an undulatory membrane ; the 

 surface is invested by a strongly developed cuticle which shows 

 distinct radiating strife, extending to within a certain distance of the 

 edge ; the hooks are from twenty-two to twenty-four in number, 

 probably chitinous, and attached proximally to the cuticle ; they 

 probably represent modified cilia. The body consists of granular 

 protoplasm, containing many globules ; of contractile vacuoles, a 

 large one is always found in the centre of the body, but sometimes 

 also a smaller one at the anterior end. The nucleus is horseshoe- 

 shaped, long, and sometimes spirally twisted at the opposite free 

 ends. 



Fission of Monothalamous Rhizopods.t — Dr. A. Gruber, in con- 

 tinuation of his studies, finds that if we make a general review of this 

 phenomenon we see (1) That in the naked Amoebae and their allies, 

 the division of the nucleus and of the protoplasm seem to go hand in 

 hand ; (2) In such forms as Lieherkuhnia, where the body is protected 

 by a secreted membrane, this may be so soft as to exert no influence on 

 the mode of division ; (3) In Gromia, Microgromia, &c., the invest- 

 ment forms a firmer capsule, which can take no share in the repro- 

 ductive act, and here the protoplasm is extended from the orifice, and 

 is at first without any nucleus ; (4) In more complex forms the thin 

 membrane around the body becomes covered by particles of sand, 



* SB. K. Bohm. Ges. Wissensch. (Prag) 1881, pp. 115-20 (1 pi.). 

 t Zeitschr. f. wiss. Zool., xxxvi. (1881) pp. 104-24 (2 pis.). 



