58 



Peridini&se 



f^-trf. 



course, be an encysted .state which has become permanent, never reverting to the motile 

 condition of the form from which it originated. Gloeodinium montanum Klebs bears a 

 sinking resemblance to Chroococcus macrococcus Rabenh. (= Urococcus insignis of most 

 authors, but probably not Ourococcus insignis Hassall), and is moreover found in precisely 

 similar habitats. As Chroococcus macrococcus is a true member of the Myxophycese, with 

 only an incipient nuclear development (see fig. 5) it would be of interest to see detailed 

 figures of the nuclear structure of Glceodinium montanum. 



Family Peridiniacese. 



In the Peridiniacese the vegetative condition is motile. The cell-wall 



is firm and hard, being built up of at least 

 three, and usually of a number of arti- 

 culated plates. There is a well-marked 

 transverse furrow composed of one or more 

 girdle plates. The external form is very 

 varied ; the cell may be globose, ovoid, 

 rhomboidal, or even flat and leaf-like, and 

 in many kinds (chiefly marine) various horn- 

 like and wing-shaped expansions are de- 

 veloped, thus greatly increasing the floating 

 capacity of the cell. 



TRANSVERSE AND LONGITUDINAL FUR- 

 ROWS. In all the Peridiniacese except 

 Podolampas and Blepharocysta, the trans- 

 verse furrow is a conspicuous feature of 

 the cell. The individual cell is thus 

 plainly divided into an apical and an 

 antapical half, the latter being usually 

 the larger. In Peridinium bipes Stein and 

 most of the freshwater species the apical 

 half is the larger, whereas in Oxytoocum, 

 Ceratocorys, Dinophysis, Amphisolenia, etc., 

 the apical half is only feebly developed. 

 The transverse furrow is approximately 

 equatorial in Peridinium africanum and in 

 P. minutum, but in most forms it takes 

 a slightly spiral course around the cell, 

 either to the left or to the right, one end 

 of the furrow being thus displaced ante- 

 riorly. It may also be somewhat deepened 

 by the development of prominent lips upon 

 either margin. 



Fig. 41. A and B, Amphisolenia spinu- 

 losa Kofoid. A, single cell viewed 

 from right side, x 140 ; B, anterior 

 extremity of cell, x 912 ; C, Dino- 

 physis ellipsoides Kofoid, view of 

 right side, x 850. ap., apical portion 

 of cell; fl.p., flagellar pore; s.sp., 

 suture spine; tr.f., transverse furrow. 

 (All after Kofoid.) 



