162 THE MASTIGOPHORA 



" nucleolar centrosome." In Nodiluca (Fig. 3) an archoplasmic 

 body situated outside the membrane accompanies the nucleus and 

 gives rise to the achromatic spindle of the mitotic figure. Mitotic 

 division of the nucleus has been described lin a large number of 

 cases taken from all the principal divisions of the group, but it is 

 certain that in some cases nuclear division occurs by amitosis 

 (Copromonas and others, Dobell [3]). Nuclear reduction in the for- 

 mation of the gametes has been observed in some cases (Trichomonas, 

 Bodo, Hexamitus, Copromonas, and others). 



Notwithstanding the great variety of structure and mode of 

 division of the nuclei in the Mastigophora, there is no evidence that 

 in any case a division of the nuclear substance takes place into a 

 somatic nucleus and sexual nucleus, comparable with the mega- 

 nucleus and micro-nucleus of the Infusoria (Heterokaryota). The 

 separation of the kineto- nucleus from the main nucleus in the 

 Trypanosomata may suggest that in this case there is a delegation 

 of special functions in connection with the flagellum to a detached 

 portion of the nucleus ; but apart from this all the Mastigophora 

 are in the strictest sense Homokaryota (Hickson). 



The life -history of the organisms comprised by the class 

 Mastigophora shows so many varieties that no general principles 

 can be laid down in this place. The life-histories of several forms 

 are described in the account given of the various subdivisions of 

 the group. The great advance in our knowledge of these forms 

 that has been made during the past few years suggests that a 

 process of gametogenesis followed by conjugation of the gametes 

 occurs in the life-histories of all the orders. 



The Mastigophora are an important component of the micro- 

 plankton of oceanic and lacustrine waters. The Dinoflagellata 

 together with the Algae of the natural order Bacillariaceae, to which 

 the former appear to be more or less closely related, are said to 

 constitute the bulk of the primary food-supply (Urnahrung) of the 

 sea [Schiitt]. 



It is customary, in the more recent treatises, to employ the 

 term Flagellata in a restricted sense, equivalent to the Lissoflagellata 

 of Lankester, with the inclusion of the Choanoflagellata. In this 

 sense also the term Euflagellata has been employed, and the 

 flagellate members of the freshwater plankton comprise Euflagellate, 

 Dinoflagellate, and Phytoflagellate 1 forms. The marine plankton 

 comprises in addition the Cystoflagellata and the Coccolitho- 

 phoridae. 



It is in order to avoid possible confusion that the term Mastigo- 

 phora, introduced by Diesing in 1866, is employed tp designate the 

 entire group of flagellate organisms. 



1 Sometimes the Phytoflagellata are comprehended within the Euflagellata, but 

 this tends to misapprehension. 



