174 GENERAL HISTOEY OF TKE I]!^FUSORIA. 



generation has not been divided the third time like the rest, but occupies by 

 itself the space which is ordinarily filled by two. Very often only six, or 

 even no more than five primordial cells are found in one envelope-cell ; but 

 then two or three of these are twice as large as elsewhere. In like manner 

 Alex. Braun figures a Pediastrum composed of fifteen instead of sixteen cells, 

 wherein one, hoAvever, is twice as large as the rest. 



"- On the whole, it is ob\ious that the mode of propagation o{ StejyJianosjyhcera 

 already examined corresponds completely to that we are akeady acquainted 

 with as formation of macroc/onidia in Chlamydococcus. It both cases it de- 

 pends upon the envelope-cell remaining unaltered, while the primordial cells 

 become divided, first into two secondary cells, and then so on in a lower 

 power of two, each of the secondary cells immediately developing two cilia, and 

 secreting over its whole surface, as do all primordial utricles of vegetable 

 cells, a delicate cellulose membrane, which, however, becomes gradually re- 

 moved further from the secreting primordial cell through absorption of water. 

 The only distinction between Chlamydococcus and Steplianosphcera arises from 

 the formation of a special envelope-cell to each individual secondary cell in 

 Chlamydococcus, while in Stephanos2yhcera all the generations produced by 

 division form one primordial cell, become enclosed by a common envelope, 

 and move away as famUies of cells. On the contrary, the developmental 

 history of Gonium, Pandorina, and Volvox agrees in all essential particulars 

 with the laws of propagation which I have just described in Steiyhanosphcera, 

 as will be shown elsewhere. We may call the mode of multiplication of the 

 Volvocinece by the general name oi propagation hy macrogonidia. 



" Another process is met with in Stephanosphcera, besides the above, and 

 which I have observed more rarely, viz. propagation hy microgonidia. In 

 this mode of multiplication the introductory processes are exactly like those 

 of the formation of macrogonidia ; in particular each primordial cell is at first 

 divided into two, then into foui% and lastly into eight secondary cells. But 

 instead of this third generation being permanent and becoming free, as is 

 usual, it not unfrequently happens that the process of division is not arrested 

 with the separation into eight — that the original primordial cell becomes 

 parted off a fourth, fifth, and even a sixth time, in the same manner, and at 

 length is broken up into a large number of cells (16, 32, 64), which naturally 

 are so much the smaller the greater nimiber of times the subdivision into two 

 has taken place (XIX. 43, 51). These little secondary cells finally become 

 totally separated from one another, Tvithout secreting an envelope-cell. These 

 little cellules — 1 shall follow the example of Alex. Braun and call them 

 microgonidia — exhibit a very active and energetic motion inside the envelojDe- 

 ceU, huiTj-ing very rapidly up and down in all directions in its cavity, pro- 

 ducing by their great number that ciu'ious swarming which Alex. Braun has 

 very aptly compared with the interminghng of a crowd of people in a confined 

 area, where every one is constantly changing his place, while the whole 

 together constantly occupy the same space. 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 where the microgonidia emerge one after another or in 

 large masses, but free and singly, into the water. Their true form may be 

 then readily detected by killing them with iodine ; they are spindle-shaped 

 and acuminated at both ends, bright green in the middle, and run out into a 

 colourless beak at each end, on the whole not imlike young Eugleyice, without 

 a trace of an envelope-cell ; the extremity which goes first in their swimming 

 bears delicate ciha ; the number of the cilia is four (XIX. 52). "WTien the 

 microgonidia reach the water they move most actively in all directions, and 



