1908] Eofoid. — Exuviation and Autotomy in Oeratium. 347 



pecially with reference to the problem of flotation as affected by 

 the extent and volume of the exoskelton. 



The term "ecdysis" or "cytecdysis" will be applied to the 

 process of shedding the entire cell wall at one time and usually in 

 a single piece, in two pieces or in a more or less intact condition. 

 The removal of the wall, plate by plate or in groups of plates of 

 small extent may, on the other hand, be designated as exuviation 

 or cytexuviation. In the first case the cell contents withdraw 

 bodily from the theca, while in the other the cell wall is cast ofE 

 in parts and with the resulting temporary combination of new 

 and old skeletal parts on one individual. 



Ecdysis. 



)-■ Occurrence i)t Di no flag Main. — In many Dinoflagellates the 

 whole theca is abandoned by the daughter schizonts after schizo- 

 gony and an entirely new exoskeleton is formed by each of the 

 two or more daughter cells or swarm spores, as for example in 

 Pyrophacus horologicum (figs. 1 and 2). At times in those gen- 

 era in which the parental theca is shed at fission the cell contents 

 may escape from the theca as a Gyrnnodi ni u in-\ike, naked spore 

 without preceding division, as in Gonyaidax, Diplopsalis (fig. 3), 

 Peridinium (fig. 4) and Glenvdinium. Subsequently, without in- 

 tervening division, an entirely new theca is regenerated to replace 

 that lost by this total and simultaneous ecdysis. The thecal 

 plates are usually not dispersed but remain adherent to one 

 another after the escape of the cell contents. Confinement in a 

 crowded plankton collection under conditions of high tempera- 

 ture, more intense illumination than normal and considerable 

 concentration of the products of plant and animal metabolism, 

 induces spontaneously this total simultaneous ecdysis in many 

 Dinoflagellates in the course of several hours after removal from 

 the sea. It also appears to occur normally in the sea to a large 

 extent in Gonyaidax pohjhedra which forms the patches of "red 

 water ' ' off the coast of Southern California in late summer. In 

 these swarms the numbers of Gonyaulax and other Dinoflagellates 

 are so great that the concentration of the products of metabolism 

 must approach that of an ordinary plankton collection, though 



