122 GENERAL HISTOEY OF THE INFUSORIA. 



tended to perpetuate the species by their ulterior development. Although, 

 like the ' macrogonidia,' they are formed within a common envelope, yet 

 each cell among them does not, as in those products, enclose itself with its 

 own tunic, and fix itself permanently within the general investment — in 

 other words, assume at once the ' still ' condition ; but the whole, after entire 

 separation from one another, become endued with vital acti^dty, and are sub- 

 sequently set free, by the dissolution or ruptm^e of the surrounding parent-ceU, 

 as so many moving zoospores (XIX. 51). The motion of these Httle bodies 

 "within the original cell is of a hurrying to-and-fro or up-and-down cha- 

 racter, and has been styled ' swarming.' On emerging from the ruptui^ed 

 ceU, each little body is seen to have a spindle-shaped figiu-e, terminated at its 

 anterior clear and usually elongated extremity by two or fom- cilia (XIX. 52). 

 In eveiy essential particular these microgonidia are homologous with the 

 motile gonidia, swarming- cells, or spores of the common Algae, such as Bry- 

 opsis, Codium, Achlya, Chcetophora , VlothrLv, Hydrodictyon, &c. Cohn's re- 

 marks on the formation of microgonidia in Stephanosphoira {A. N. H. 1852, x. 

 p. 346) may elucidate this subject stiU fiu'ther. He says, " While, in the 

 formation of macrogonidia, the secondary cells become surroimded by a 

 common envelope and are not free (as an entii-e connected family of ceUs 

 arranged according to a definite law), in the mode of propagation of micro- 

 gonidia the little secondary ceUs finally become totally separated from one 

 another without secreting an envelope-cell; and in this way each of the 

 eight primordial cells of the perfect Steplianosplicera is broken up into 32 to 

 64 independent, green, elliptical or spindle-shaped corpuscles, which then 

 separate from one another, commence an independent and active motion, and 

 fill up, in great numbers (as many as 256-512), the common parent envelope- 

 cell (XIX. 51). . . . The crowding-in among each other of the microgonidia of 

 Steplianosph<xra presents a picture fixing the attention in the highest degree : 

 sometimes the cellules are scattered in a few large masses — then they unite 

 again into a knot in the middle — every moment the general aspect varies. 

 At length the common envelope is ruptured," and they escape in masses 

 into the water. *' Their true form may then be detected readily by killing 

 them with iodine ; they are spindle-shaped and acuminated at both ends, 

 bright green in the middle, and run out into a colouiiess beak at each end — ■ 

 on the whole not unlike young EugJence, without trace of an envelope-cell 

 (XIX. Q2)y On reaching the water their movements are most active, and 

 then rapidly disperse out of sight. These bodies are true primordial cells, 

 *' that is, primordial utricles resembling cells, organized exclusively of co- 

 loured protoplasm, mthout any cell-membrane." 



Upon a general survey of development by gonidia, Cohn remarks {A. N. 

 H. 1852, X. p. 403) — " Abstracting the differences which may always be 

 shown between two genera, we detect the same law of development in Hy- 

 drodictyon as in Stephanosphcvra : the biciliated, less numerous macrogo- 

 nidia arrange themselves into a family of cells abeady within the parent-ceU, 

 according to the character of the given conditions of the two genera, — the 

 cell-family being active in the Volvociueae and immoveable in the Proto- 

 coccaceae ; while the more numerous, more actively-moving microgonidia 

 with four cilia leave the parent- cell and enter upon a metamorphosis, the re- 

 trogradation from which to the normal type of the genus has not been ob- 

 served yet here, or indeed in the microgonidia of any of the Alga3," It may 

 be conjectui-ed that these latter pass into a resting state, prior to any further 

 development ; for both Cohn and Braun have witnessed this change tu 

 Chlamydococcus pjluvicdis. 



The formation and escape of microgonidia have been observed by many 



