THE PHiEOPHYCEATf ZOID 5 



colour, giving no carotin-reaction {Pelvetia, Durmllcea) ; but in no 

 ease can it be said to be wholly eliminated. The function is un- 

 doubtedly that of light-perception, while in ontogeny it is always 

 derived from a localized area in a chloroplast (Yamanouchi), and the 

 orange pigment ("carotin ") apparently indicates that the cytoplasm 

 must be stimulated by the absorption of violet rays. 



The zoids in no case swim backward (as is normal for an anterior 

 tractor-mechanism) ; but as they slow down they move in larger 

 to smaller circles as the expression of the loss of steering-power and 

 some sense of direction. Apart from any question of nutrition, the 

 flagellum acts as a tactile sensitive organ ; thus in response to 

 stimulus of contact, as in collisions with foreign objects, the zoid may 

 slightly change it course (cf. Jennings, 1904). This sensitiveness 

 is emphasized by " chemo tropic " phenomena, and apparently repre- 

 sents the factor of greatest significance in the employment of the zoid 

 as a *' sexual " cell. 



Thus in Cutleriacese (Yamanouchi) the anterior flagellum is the first to 

 come out of the gametangium, and first makes contact with the other 

 gamete. The spinning of the oospheres of ¥ucxis and Ascophyllum in 

 fertilization is apparently the expression of the activity of the shorter 

 anterior arm in the antherozoids of these types, when the longer trailer ia 

 entangled in the oosphere. In other genera (Halidrys, Himanthalia) the 

 sperms entangled by the longer driving anterior tractor merely gyrate on 

 the point of contact. 



Euglenoid movement is always retained, and the larger zoids bend and 

 curve, or " nose about," in a very suggestive mouse-like manner, exhibiting 

 contractility all over the body-surface as a general property of the 

 cytoplasm. 



Amoeboid movements are more rare ; but irregular protrusions of pseudo- 

 podia-like nature may follow benthic attachment to the substratum in 

 germinating zoids of Myrionema. 



Exact data for the speed attained are wanting ; it would appear 

 that 1-2 ft. per horn* is a fair rate for a 7 yu zoid ; but active units 

 do better than this for short distances across the field of the micro- 

 scope. As seen under the microscope the movements are wholly 

 erratic, like those of a swarm of ants, or mice in a box ; and it would 

 be absurd to interpret the motor mechanism only in terms of such 

 observations. Under the low power it is possible to time zoids along 

 the scale of the micrometer eye-piece ; and a moderate estimate for 

 gametes of Lajninaria saccharina gave 1 mm. in 5 seconds, or over 

 2 ft. an hour ; gametes of Ectocmyus are half as quick again. The 

 large zoids of Pylaiella fulvescens, according to Sauvageau, do not 

 move faster than a Diatom. The rate again probably bears a relation 

 to temperature and oxygen-supply, as well as to the condition of the 

 material. Measurements are difficult for longer distances, as the 

 field of the low power is only 2 mm. diam. : Sauvageau records zoids 

 crossing a 5 mm. drop in about a minute, or approximately a foot an 

 an hour. 



Records of the duration of the motility are vitiated by observa- 

 tion in water in which a full oxygen-supply is not maintained (as 



* Jennings (1904) ' Behaviour of Lower Organisms.' 



