74 Peridiriiex 



in certain genera of the Peridiniacese, but the details of their formation and 

 their ultimate fate require further investigation. 



Zederbauer ('04) has described a presumed sexual reproduction in 

 Ceratium hirundinella by the conjugation of two individuals and the 

 formation of a zygote (fig. 55). He states that the two cells become 

 attached by their ventral areas in such a manner that their respective 

 anterior and posterior extremities point in reverse directions. Then from 

 each individual a conjugation- vesicle is extruded through the nagellar-pore, 

 into which the protoplast gradually passes. The fusion of the two proto- 



Fig. 55. Presumed conjugation of Ceratium hirundinella O. F. M. A and B showing two positions 

 of conjugating (?) cells ; C, supposed zygote (probably a cyst), x 660 (after Zederbauer). 



plasts (gametes) results in a rounded zygospore, which becomes transformed 

 into a three-horned resting-spore. In contrast to these statements, Entz 

 ('07) describes the zygote as being formed within one of the old walls, which 

 is in consequence burst open. Moreover, he states that only the nucleus 

 of the one gamete passes into the other, the cytoplasm of the first gamete 

 being lost. Neither of the nuclei undergoes any change, nor is there any 

 nuclear fusion. The observations of Zederbauer and Entz are somewhat 

 contradictory, and if conjugation does occur in the Peridiniacese it is of very 

 rare occurrence, and still requires full investigation 1 . At present there is not 

 sufficient proof that conjugation does exist in the Peridiniacese. 



1 Two doubtful cases of conjugation have been recorded in marine species of Ceratium : one 

 by Pouchet in Ceratium fusus, and the other by Kofoid in C. biceps. There are also several 

 records of conjugation, all very doubtful, in Glenodinium and a marine species of Peridinium. 



