Pyrocystaceae 55 



In the peripheral zone of the protoplast, Polykrikos Schwarteii Biitschli 

 and Pouchetia armata Dogiel are provided with nematocysts. It is 

 by no means easy to explain how these structures are functional in uni- 

 cellular organisms of such a type. It is easy to state that they play a part 

 in nutrition, but there is no evidence to show that the nutrition of these 

 organisms is other than saprophytic. Possibly they act purely as protective 

 structures. 



The organism known for a long time as Pyrocystis lunula (fig. 40 B and G) 

 has quite recently been transferred by Klebs ('12) to the Gymnodiniacea; 

 and made the type of a new genus, Diplodinium. This change is made as 

 the result of the recent work of Apstein ('06) and Dogiel ('06), the genus 

 being based upon the fact that there are two successive encysted stages in 

 the life-history. The primary cysts are large and globose, the contents 

 dividing to form two, four, or eight secondary cysts of a crescentic or lunate 

 form, which are set free by the rupture of the old wall. The secondary 

 cysts now produce by successive divisions of the protoplast either 8 or 

 16 flagellated organisms of the Gymnodinium-iype. After 'swarming' for 

 a time within the wall of the lunate cyst, they become quiescent and surround 

 themselves with a membrane ; but nothing is known of the development of 

 the primary cysts from these small flagellated cells. 



Klebs has placed those Gymnodiniums which produce thick- walled, 

 sublunate, and often horned resting-cysts in a genus which he describes as 

 Cystodinium. He has also established a further genus, Hypnodinium, in 

 which the division of the encysted protoplast produces two naked cells with 

 the Gymnodinii(m-\ikQ furrows, but no flagella. These are set free, and 

 grow into new cysts without ever becoming motile. 



The present author does not agree with Klebs in the transference of 

 Glenodinium to the Gymnodiniacese (see foot-note on p. 61). 



Family Pyrocystacese. 



The Pyrocystacese is represented by the solitary genus Pyrocystis, which 

 was originally discovered during the voyage of the "Challenger." The 

 organisms often occur in great abundance in the pelagic plankton of tropical 

 and subtropical seas, wherever the temperature of the water is over 68 or 

 70 F. They are strongly luminous, and there is little doubt that the 

 diffuse luminosity of the open sea in warmer regions is mainly due to species 

 of Pyrocystis. When floating quietly they give out no light, but agitatiqn 

 of the surface water causes them to shine out as points of bluish light. It is 

 probable that the luminosity is due to the oxidation of certain substances, 

 such as lecithin, cholesterin, ethereal oils, etc., which are contained within 

 the cell. Agitation of the water increases the rapidity of oxidation, either 

 by augmenting the supply of oxygen or by raising the irritability of the 



