ARCHER — ON STEPHANOSPUiERA PLUVIALIS (COHN). 155 



pressed figure, gradually expands in the polar direction until the sphe- 

 rical form is attained — the primordial cells meanwhile acquiring their 

 mature appearance and structure. Thus each parent Stephanosphaera 

 can normally give rise to eight young Stephanosphaerae, though families 

 of but four cells occasionally, though rarely, occur (and still more rarely 

 families of five, six, or seven), through arrested subdivisions of the pa- 

 rent primordial cells ; whilst I have once or twice met with families of 

 sixteen cells, arising from the " transition generations" (Nag.) being 

 carried one stage further — that is, the (normally) eigbt cells each divid- 

 ing once again before arriving at the fully formed or "mature stage" 

 which may in similar manner be called the " permanent generation" 

 (Nag.). 



A second change connected with the propagation consists in the 

 disassociation from the hyaline sphere, arid the contraction of the pri- 

 mordial cells, as before, into rounded bodies ; but in this instance this 

 is followed by the formation round each of a special cellulose wall, 

 through which protrude two cilia, by the agency of which these Chlamy- 

 domonas-like cells swim vigorously about, at first within the old parent 

 globe, afterwards outside it, when they have made their escape by its 

 destruction. Finally these Chlamydomonas-like bodies come to rest, 

 lose their cilia, and assume a Protococcus-like appearance, or these Pro- 

 tococcus-like resting cells may apparently be formed without an inter- 

 mediate motile Chlamydomonas-like state. These Protococcus-like cells 

 have the power of increasing in size after their formation, and before any 

 further development. Cohn and Wichura's researches have demon- 

 strated the remarkable fact, that not only are these capable of revival 

 upon being covered with water after complete and lengthened desicca- 

 tion, but that such desiccation is absolutely necessary to induce further 

 changes in the direction of the renewal of the Stephanosphaera-globe. 

 A few hours after being remoistened the cell-contents of these resting- 

 sporcs become divided into two, then into four (possibly sometimes eight) 

 daughter-cells, the cellulose wall vanishing. These daughter-cells be- 

 come biciliated, and presently one by one separate, and swim freely 

 away as so many pear-shaped zoospores. Afterwards, coming to rest, 

 they acquire a membrane which at first closely surrounds the contents; 

 but presently expands, and, standing off, leaves the body of the primor- 

 dial cell in the middle, which protrudes a pair of cilia through the wall, 

 thus again assuming a Chlamydococcus-like appearance. The contents 

 often in this stage present a number of hyaline frequently branched or 

 forked projections in various directions from the outer protoplasmic layer 

 (like those from the opposite ends of the primordial cells of the mature 

 plant), and which touch the inner surface of the cellulose wall. But 

 after an interval these Chlamydococcus-like structures begin to divide ; 

 if the protoplasmic processes exist, they are previously drawn in, and 

 the primordial cells become rounded — a series of self-divisions sets in, 

 similarly to those of the primordial cells of the perfect Stephanosphacra 

 in the first mode of propagation, the cilia become lost, and the process is 



