396 MEMOIRS OF THE UNIVERSITY OF CALIFORNIA 



elongate barrel-shaped, the extreme length reached in the eight-zooid stage being 

 4-5 transdiameters at the widest part near the middle. The girdle is usually 

 transverse with its posterior displacement occurring at its distal extremity. 



The body is without appreciable torsion, each zooid having the same orien- 

 tation as its neighbor, with their sulci connected at their extremities and forming 

 a continuous channel along the ventral face of the colony. The sulcus usually 

 terminates near the right side of the apex of the j^roximal zooid and at the 

 antapex of the distal one. 



The nucleus of Polyhrikos has the beaded chromatin strands characteristic 

 of the Dinofiagellata generally and is without a distinct perinuclear zone. The 

 number of nuclei in the colony is usually half the number of zooids. 



The color of the cytoplasm of Polykrikos varies from a greenish tint, or 

 ahnost colorless, to faint, diifuse rose, and is probably subject to considerable 

 modifications through the food ingested by the organism. It is not improbable 

 that the rosy tint results from feeding upon rose or red colored forms, like 

 Peridinium divcrr/ciis and P. conicum, usually abundant in the plankton ^^-ith it. 

 Noctihica seinfilhms, feeding on the same plankton, exliibits a similar var^ang 

 rosy tint in its color. The presence or absence of this color is one of the char- 

 acters which Bergh (1881&) uses in separating his Polykrikos auricidaria 

 from Biitschli's species (1873), P. sclucartzi, a distinction which is apparently 

 not well grounded. 



Pohikrikos is holozoie in nutrition, as the abundance of individuals found 

 with recognizable organisms in the cytoplasm indicates. These may include 

 almost all the small organisms occurring in the plankton Avith it, both metazoan 

 and protozoan. 



The nematocysts of Polykrikos are found in all individuals without ex- 

 ception. The.v vary considerably in number and arrangement and have been 

 observed to shift their position during the spasmodic plasmatic movements 

 sometimes seen in the interior of the organism, and are often crowded to per- 

 ipheral locations by the relatively large food masses sometimes ingested. They 

 are not, when developed, fixed organs with definite locations, but may occur in 

 any part of the body. Chatton (1914f) has demonstrated their origin from the 

 serially arranged centrosomes at the right of the nuclei. 



Division in PoJijkrikos is accomplished by the formation of new girdles 

 between the already existing ones, followed by a division of the nuclei. A 

 division of the colony is accomplished by a constriction of the body along the 

 line of separation of the middle zooids, and may occur in four, eight, or sixteen 

 zooid stages. 



Distribution 



Polijkrikos occurs along the Avestern coast of Europe, as far north as ISTor- 

 way. in the Mediterranean, and along the coast of California, giving it a known 

 distribution that is exceeded in its breadth by only a few species among the 

 Gymnodinioidae. Its occurrence is thus confined largely to warm temperate 



