22 MBMOIKS OF THE UNIVERSITY OE CALIFORNIA 



a standstill. At the opposite jDoles of the nuclei are large, conspicuous 

 centrospheres with astral rays surrounding- them (fig. E, 1, c). The relatively 

 huge nuclei contain several nucleoli and are trausversed by filaments, ])lasmo- 

 dendrites (fig. E, 1, pins.), which are the remains of the nuclear spindle fibers 

 formed by the division of the centrosj^here or eentrosome. 



These peculiar structures are found in the sporocytes of all ages, but dis- 

 appear with the maturity of the spore. In the last sporocyte divisions the 

 centrospheres and achromatic figures disappear (figs. E, 2, 4) and a simple type 

 of "Haplomitose" results. 



In this still incomplete study of Chatton interesting questions concerning 

 the complete stages of mitosis and nuclear development are raised, both in the 

 parasitic and in the free-living forms. The difference between the two types 

 may be due, as he suggests, to the influence of hjq^ernutrition consequent on a 

 parasitic mode of life within the digestive canal of pelagic copepocls. A com- 

 parison of free-living and parasitic forms elsewhere among the Protozoa out- 

 side of the Sporozoa, where free-living forms are not found, does not suggest 

 this as a probable solution. There are suggestions in some of Borgert's figures 

 (1910, pi. 2, figs. 12-14) of an archoplasmic structure corresponding to spindle 

 and polar regions. It may well be that further studies on these forms, Avith 

 more critical cytological differentiation, will demonstrate the presence of such 

 structures and reveal a closer similarity between the processes in the free-living 

 and parasitic forms. 



PustTLES. — A well developed pusule apparatus is usually present in all the 

 dinoflagellates. It consists essentially of a sacklike vacuole connected with 

 tlie exterior by a slender canal opening into a flagellar pore. The fluid con- 

 tained within it has a delicate rose or pale salmon pink color. The exact 

 relations of the flagella and their blei^haroplasts to the walls of the canal are 

 uncertain. Their insertion seems to l)e a short distance below the oi^ening of 

 the i^ore. Two pusules are usually present, one opening anteriorly into the 

 anterioi" flagellar pore, the other opening posteriorly into the posterior one. 

 These two i^usules may occasionally be united by a slender canal, forming a 

 long channel opening at either end into a flagellar pore. In many species, par- 

 ticularly in the thecate forms, one or two branches or accessory pusules are 

 formed as offshoots from the main collecting pusule. These are more or less 

 temporary and not as constant in their occurrence as the main pusule. 



In the thecate forms the pusules are usually relatively huge, often with 

 accessory branches. Their size and their pinl^; color combine to make them the 

 most conspicuous features of many of the species. For this reason they at- 

 tracted the attention of earlier biologists, and their structm-e and homologies 

 were the subject of some speculation. Biitschli (1885) compared them to the 

 contractile vacuoles of other better known Protozoa, and in this he was followed 

 by Schiitt (1895) in his comprehensive discussion of the subject. The latter 

 investigator also pointed out the difference between the ordinary fluid vacuoles 



