KOFOID AND SWEZY: UNARMORED DINOFLAGELLATA 



21 



the ordinary trophozoite stage (pi. 8, fig. 83; ])1. 10, fig. 114), witliout evidence 

 of an intervening stage in which the nionilit'oru) chromatin threads or chromo- 

 somes are broken up. 



Attention must be called to the appearance of the nucleus, as figured by 

 Borgert, also by Lauterborn and Jollos, Ijefore the onset of division. The 

 chromatin here lies iml)edded as minute granules in the meshes of a reticulum 

 that fills the entire nucleus, usually with one or more large nucleoli also present. 

 This is in marked contrast to the appearance of the nucleus of the living organ- 

 ism. In the hundreds of individuals observed by us the nuclei presented a 

 fairly uniform and characteristic appearance. In no instance has a network 

 been visible and in only a very few cases have the granules been arranged in 

 other than definite linear series. One of these is Gijrodiuiuni coraUinuni, where 

 a modification of the usual type of nucleus is present in the form of a sur- 

 I'ounding alveolate zone (j)! 10, fig. 117). In a few cases the nuclei seemed 

 homogenous, but usually they presented the distinct nioniliform threads as 

 shown in our figures. In a few instances these have been omitted in both the 

 line drawings and the colored plates to avoid a too great mass of detail. With 

 proper lighting conditions this structure can usually be demonstrated in the 

 living organism. 



The change of these linear threads to the minute granules enmeshed in a 

 reticulum in the stained specimens may be due solely to the action of the fixative 

 used in preserving the material. That a very great change takes place in proto- 

 plasm as well as nucleoplasm in the action of any chemical upon them is evident 

 to any one working i;pon the living, in connection with stained, material of any 

 protoplasmic body. 



Chatton (1914rt) has made per- 

 haps one of the most important 

 contributions to this question of 

 nuclear structure in the dinoflagel- 

 lates in his work on the parasitic 

 forms. In Blastodiiiium crassiim 

 he figures (fig. E) details of nuclear 

 structure, w^hich clearly point to a 

 greater complexity in the process 

 of mitosis than has yet l)een dem- 

 onstrated for the free-living dino- 

 flagellates by any other investigator. 



The appearance of the tropho- 

 cyte, as Chatton has termed this 

 peculiar, binucleated stage of the 

 life cycle of BI((stodi)u'i(i)i crassion 

 (fig. E, 1), represents a dinoflagel- 

 late in the late metaphase in which 

 further development has come to 



plas.. - 



c 



c. 



. c. 



Fig. E. Blastodinium crassum Chatton. After Chat- 

 ton (1914a, figs. 1-4). Abbreviations: c, centrospheres; 

 H., nuclei; plas., plasmodendrites. 1. Trophocyte in nor- 

 mal ^•egetative phase. 2. Sporocyte with remnants of the 

 centrospheres still visible. 3. Sporoeyte farther advanced 

 with centrospheres completely obliterated. 4. Sporoeyte 

 of nearly last division stage. X f 



