Grt/mnodiniaceas 



53 



B 



Fig. 38. A, longitudinal division of (jyiniio- 

 diniiim viride Penard, the fission almost com- 

 pleted ; B, transverse fission of G. rufescens 

 (Penard) Lemm. showing the dividing nucleus 

 (after Penard). Ouly the longitudinal flagella 

 are shown, x about 450. 



nutrition of the coloured forms is normally holophytic, but in certain cases 

 there appears to be in addition a 

 truly animal-like method of taking 

 up solid food by means of pseudo- 

 podia protruded from the region of 

 the transverse furrow. This occurs, 

 according to Zacharias, in Gymno- 

 dinium Zachariasi Lemm. Some 

 forms, such as Gymnodinium fucorum, 

 G. spirale, etc., are without chro- 

 matophores and lead a saprophytic 

 existence. A few parasitic forms 

 have also been described, notably 

 Gymnodinium parasiticum Dogiel, 

 G. Pouchetii Lemm., and G. roseum 

 Dogiel. The first-named lives during 

 part of its life-history within the 

 eggs of Copepods 1 . 



In the colourless forms Gymno- 

 dinium Vorticella Stein, G. helveticum 



Penard, and Spirodinium hyalinum (Schill.) Lemm., the nutrition is stated 

 to be completely holozoic, but this assertion requires very careful con- 

 firmation. In the last-named, the organism loses its flagella and becomes 

 amoeboid before the ingestion of solid food-substances. In Gymnodinium 

 Vorticella Stein, the ingestion of food takes place while the organism is 

 active, and the food-remains are thrown out when in the resting-state 

 (Dangeard, '92). 



Multiplication occurs in most cases by cell-division while the organisms 

 are in the motile state. The division is usually longitudinal, although in 

 a few cases, such as in Gymnodinium rufescens, it is transverse (fig. 38 B). 

 Unfavourable conditions of existence rapidly bring about a quiescent, en- 

 cysted state, in which multiplication may sometimes occur. In this non- 

 motile state the cell may be surrounded by a thick gelatinous envelope 

 (as in Gymnodinium Zachariasi) or only by a thin membrane (as in Hemidinium 

 spp. and Gymnodinium fucorum). After the division of the parent-cell the 

 two daughter-cells are set free either by dissolution of the gelatinous 

 envelope or by the bursting of the thin membrane. A resting-state with 

 thick cellulose walls has occasionally been observed in some forms. 



1 E. Chattou (Complex Rendun Aead. Sc. Paris, cxliii, 1906; ibid, cxliv, 1907) has also 

 described several parasitic species of the genus lllastodinium, which he regards as the type of 

 a new family of the Peridinieas. These organisms are parasites upon various pelagic Copepods 

 and Appendicularians. 





