604 ORDER HETEROTRICHA. 



cannot at present be determined. The generic group, even as more explicitly cir- 

 cumscribed by Ehrenberg and later authorities is, however, by no means so 

 clearly defined as might be wished. Under this title are indifferently included 

 animalcules that live, as indicated in the foregoing- diagnosis, an entirely free-swim- 

 ming or pelagic life, and others whose loricae, like those of Vaginicola or Folli- 

 culina, are permanently attached to water-plants or other submerged objects ; the genus 

 indeed, as defined by Eichwald, is erroneously represented as composed entirely of 

 such sedentary forms. In recognition of the essential difference that subsists between 

 these respective pelagic and sedentary types, it has been considered desirable to 

 separate from Tintinnus all those animalcules that belong to the last-named 

 category and to confer upon them the new generic title of Tintinnidium. The 

 genus Tintinnus, as limited only to the free-swimming or pelagic forms, still presents 

 structural characteristics upon which modern investigators have as yet arrived at a 

 by no means harmonious interpretation. Although Claparede and Lachmann have 

 succeeded in demonstrating that the entire cuticular surface in the majority of the 

 species examined by them, inclusive of the type form T. inquilinus, is clad with fine 

 vibratile cilia, as in Stentor, Follicularia, and other Heterotricha, no such finer sup- 

 plementary cilia were observed by the founder of the genus or other more recent 

 authorities. Even Stein, whose personal acquaintance, however, is apparently 

 limited only to the two species Tintinnus inquilinus and Tintinnus (Tintinnidium} 

 fluviatilis, failed to detect the presence of these cilia, and has in consequence referred 

 the genus, together with Tintinnopsis, to the order of the Peritricha. The positive 

 evidence afforded by Claparede and Lachmann's investigations nevertheless out- 

 weighing that of a negative nature only as produced by Stein in connection with 

 this structural characteristic, the author has felt constrained to support the views of 

 the first-named authorities, and to concede to the genus a corresponding position 

 among the Heterotrichous order. It is at the same time by no means improbable 

 that many Tintinnoid forms exist which differ from the typical members of the 

 genus through the absence of a cuticular ciliary clothing, for which it will be requisite 

 to institute a new generic title, allocating them to the order of the Peritricha. The 

 Tintinnus subulatus of Ehrenberg is not improbably of this number. 



All the known representatives of the genus Tintinnus, as here defined, inhabit 

 salt water, and are notable for the extraordinary rapidity of their movements. 

 Placed under the microscope they dart to and fro across the optic field with the 

 swiftness of an arrow, a considerable amount of difficulty being necessarily involved 

 in the apprehension of their more minute structural characters, and it is only 

 indeed in examples that have become entangled among other objects present, or 

 are held tight by compression between the slide and covering-glass, that these 

 details can be sufficiently investigated. Through the researches of Claparede 

 and Lachmann a very considerable addition has been made to the number of 

 species included in the genus Tintinnus by Ehrenberg. It is necessary, however, 

 to remark that in a large number of them the empty sheaths or loricae alone 

 have been observed, and it is therefore quite possible that certain of these struc- 

 tures may hereafter be found to belong to such other pelagic loricate types as 

 Codondla, Tintinnopsis and Dictyocysta. In their adoral ciliary system and general 

 contour the animalcules of Tintinnus correspond to some extent with those of the free- 

 swimming illoricate Peritrichous genus Strombidium, with which again they are still 

 more intimately united through the newly introduced and essentially Heterotrichous 

 type Strombidinopsis. 



Tintinnus inquilinus, Mull. sp. PL. XXXI. FIG. 15. 



Lorica subcylindrical, diaphanous, four or five times as long as broad, 

 slightly attenuate posteriorly, the extreme ends abruptly truncate, anterior 

 margin smooth, not everted; body of animalcule often fixed to one side 

 instead of to the bottom of the lorica, elongate-conical, pedicle not quite 



