EXTERNAL GEMMATION. 87 



entire obliteration of the primary oral system, two new ones subsequently 

 appearing in its place. 



In a third, but comparatively very small number of Infusorial forms, 

 neither a transverse nor longitudinal mode of fission is met with, but 

 one that takes an entirely oblique direction. The Ciliate genera Stentor 

 and Lagenophrys, and the new Flagellate type described in this volume 

 under the title of Anchomonas sigmoides, are among the most noteworthy 

 examples of this somewhat aberrant process. Although it usually happens 

 that all of these various phenomena of multiplication by simple binary 

 division now enumerated are accomplished during the active life of the 

 animalcule, it not unfrequently happens that a quiescent or encysted con- 

 dition, as described at page 63, is specially entered upon for the fulfilment 

 of this purpose. Illustrations of this developmental phase are afforded 

 by Amphileptus meleagris, Otostoma Carteri, Etiglena viridis, and many 

 other Flagellata. The appearances exhibited in certain of these cases 

 more nearly coincide, however, with the sporular conditions discussed later 

 on. In all instances, it would seem that the duplication of the in- 

 fusorial body by the process of binary division is, as with the similar 

 multiplication of the cells of ordinary tissue structures, accompanied, or 

 rather preceded as an initial act, by the subdivision of the nucleus or endo- 

 plast. Other organs, such as the contractile-vesicle and oral or anal structures 

 and appendages, are not so divided, but are independently developed in 

 that moiety in which previous to subdivision they were unrepresented. 



External and Internal Gemmation. 



The phenomenon of reproduction by " external gemmation," although 

 represented in tolerable abundance among the present organic group, occurs 

 by no means so generally as was formerly supposed. Up to within a com- 

 paratively recent date that larger or smaller bud-like body, not unfrequently 

 found attached to the lateral periphery of various members of the Vorti- 

 cellidae, and also the secondary pendent zooid, which, while first attached 

 to, finally breaks away from the parental stem, were premised to be 

 examples of such gemmation. In both of these cases, however, the so-called 

 gemmule is derived through a modification of the process of binary fission, 

 previously described, from an ordinary zooid, though in the former instance 

 the association is fortuitous, and, as hereafter shown, has a peculiar 

 significance. Instances of true external gemmation are, nevertheless, 

 afforded by such types as Spirochona, and apparently also Lagenopkrys 

 among the Ciliata, while among the Tentaculifera, Hemiophrya (Podophrya) 

 gcinmipera and the various species of OpJiryodendron, more especially 

 O. multicapitata, supply prominent examples of this phenomenon. In 

 the majority of the cases mentioned it has been recently demonstrated that 

 a diverticulum of the endoplast accompanies the outgrowth of the body- 

 substance, forming the characteristic bud, and becomes separated off and 



