FUCACE^E. 85 



in a capsule of seawater until it became turbid owing to their number. If on 

 examination the antherozoids proved to be active, small quantities were added 

 to the vessel containing the oospheres. ('96, p. 480.) 



When vigorous antherozoids (1. c., '98, p. 631) are transferred to vessels con- 

 taining healthy oospheres they at once congregate around them, and attaching 

 themselves to the periphery of the eggs, cause the well-known movements by 

 lashing the water with the free cilium. But, as Thuret noticed, fertilization can 

 often be effected without any whirling movement taking place, and we have 

 observed perfectly normal germination to follow on the addition of apparently 

 inactive antherozoids to the oospheres. 



There seems to be a marked difference between the degree of attrac- 

 tion exerted on the antherozoids by the egg-cells under different condi- 

 tions. Thus, when the extruded products have been long exposed to 

 a moist atmosphere, so that all the membranes have become deli- 

 quescent, the spermatozoids are hardly influenced by the oospheres. 

 On the other hand the oospheres which still retain their walls become 

 covered with spermatozoids. 



The behavior of the spermatozoids in the genus Halidrys is of 

 especial interest in this connection, and I quote again from the same 

 authors (1. c., '98, p. 633): 



On watching the behavior of the antherozoids when swimming amongst the 

 oospheres, they are seen to attach themselves to the surface of the eggs by one 

 cilium, whilst they maintain a circular or gyratory movement around their 

 point of attachment. Most often there is a number a dozen or more of 

 these groups, each consisting of 4 to 12 antherozoids, distributed over the sur- 

 face of each oo'sphere. The movement is always in the clockwise direction, 

 and the chromatophore is on the end of the antherozoid remote from the egg. 

 The rate of gyration is fairly rapid, 40 to 50 complete turns being made in a 

 minute. After this has been going on for a while the egg itself evinces 

 a change, swelling somewhat and appearing more transparent than before. 

 Sometimes movements of vacuoles may be discerned, and even the position of 

 the nucleus may change. These alterations ensue as the definite result of the 

 stimulus in some way given by the antherozoids themselves. . . . Sud- 

 denly the antherozoids are seen to leave the egg like a crowd of startled birds, 

 or else they become quiescent, and these phenomena are immediately followed 

 by a great change in the egg itself, which becomes warty and covered with 

 conical projections. From each papilla a fine thread projects, consisting of a 

 moniliform series of droplets, and the antherozoids may sometimes be observed 

 attached to these threads. After the lapse of a few (3 to 5) minutes the egg 

 resumes its spherical form whilst at the same time its diameter becomes 

 smaller. Still later the fine threads also disappear, whilst the egg regains its 

 original size. As long as the antherozoids are in active motion on the surface 

 of the egg, the latter exhibits a scarcely perceptible rocking movement and is 

 free in the water, but during the events which have just been narrated it 



