588 FERTILIZATION 



most of them are too fragmentary or are supported by too little evidence 

 to be discussed here. 



An extremely interesting case has recently been reported by Diwald 

 (1938) in Glenodinium lubiniensijorme. In this form, four flagellated 

 isogametes are produced by the subdivision of each parent protoplast, 

 and these gametes will copulate only with gametes of certain other 

 clones. The obvious question is, of course, what is the nature of the 

 difference between these "'_|_" and " — " strains, a difference which in- 

 hibits their copulating among themselves or stimulates them to copulate 

 with gametes of the other strain? This problem is yet to be solved, but 

 it is similar to that found in Paramecium aurelia by Sonneborn (1937) 

 and in P. bursaria by Jennings (1938). Diwald states that after fertili- 

 zation the zygotes rest, then germinate and undergo two reduction divi- 

 sions to form a "tetrad" of four potential individuals, only one of which, 

 however, usually persists. This is the only described case of zygotic 

 reduction outside the Telosporidia, with the possible exception of the 

 amoeba Sappinia diploidea (see p. 595 below). A reasonable doubt re- 

 mains, however, as to Diwald's interpretations. He gives no chromo- 

 some counts that would support his contention, and any assumption of 

 chromosome reduction not based on determinations of chromosome 

 numbers before and after reduction, especially in such an unusual case, 

 is open to serious question. Dinoflagellates are not popular subjects for 

 cytological investigation at the present time, but perhaps the work of 

 Diwald will stimulate further research in this group. 



In Ceratium hirundinella fertilization is accomplished in a way simi- 

 lar to that of the filamentous algae, according to the description of Zeder- 

 bauer (1904). Two flagellates come together, the protoplasm of each 

 extrudes from the lorica and makes contact with that of the other. The 

 two masses now copulate, forming a zygote outside the loricas. Zeder- 

 bauer observed these protoplasmic fusions only in the living state, so 

 his account leaves much to be desired in the way of cytological details 

 on which to base sound conclusions. 



Chatton and Biecheler (1936) have more recently reported fertili- 

 zation by slightly anisogamous gametes in the parsitic form Coccidinium 

 mesnili. 



In NoctHuca scintHlans {m/liaris) gamete formation has been re- 

 peatedly reported. In recent accounts Pratje (1921) could find no 



