146 THE ROYAL SOCIETY OF CANADA 



other hand, the breeding season of Solaster may be much later at 

 St. Andrews than in Great Britain (as is the case with a number of other 

 forms) and the sperm may have ripened earlier than the ova, as was 

 observed in the case of Asterias in 1917. 



The Asterias sperm and ova were normal and ripe. The ova 

 matured within 30-40 minutes after being placed in sea water. As 

 the spermatozoa were rather sluggish, a few drops of ammonia were 

 added to the water. Sperm thus treated became very motile, and 

 when added to the ova of its own species induced a development of 

 from 90 to 100 per cent. 



On July 22, 1917, at least two weeks before Bipinnaria were 

 found in the plankton, male Asterias were procured whose testes 

 were swollen and large and had every appearance of being mature. 

 The spermatozoa, however, when introduced into sea-water remained 

 motionless. On adding enough ammonia to the water to raise the 

 NH3 concentration to 0055 grams in 100 c.c, the sperm became 

 motile and capable of fertilization. A lowering of the concentration 

 to 0-0045 grams in 100 c.c. stopped all movement. Fresh sea water 

 was found to contain normally 0-002 per cent NH.3. Later in the 

 season (early August) spermatozoa were active in normal sea water. 

 It is known that increase in the hydrogen ion concentration will inhibit 

 the movement of spermatozoa and cilia. Possibly the testis is acid 

 owing to the presence of a relatively great amount of CO2 produced 

 in the active metabolism of the developing sperm. The mature 

 sperm would thus be existing in an anaesthetized condition. The 

 addition of ammonia neutralizes the inhibiting effect of the CO2 and 

 renders the mature sperm motile. In a fully ripened testis, the de- 

 veloping process has largely ceased and the acidity has had a chance 

 to be dissipated. For such a testis the alkalinity of normal 

 sea water is sufficient to activate the spermatozoa. The Solaster 

 testes, according to this assumption, were not fully ripe, since the 

 spermatozoa of Solaster were quite motionless in sea water and 

 were activated only by being placed in alkaline sea water. 



Solaster spermatozoa, which had been thus activated, were 

 poured into bowls containing mature Asterias ova. In one and one 

 half hours fertilization membranes appeared in about 20 per cent 

 of the eggs. Their polar bodies were all outside the fertilization 

 membrane. In the case of the control (Asterias sperm x Asterias 

 ova) the polar bodies were all inside the fertilization membrane. 



The difference in the position of the polar bodies is 

 dm'', the difference in time of the initiation of fertilization. 

 In the cross-fertilized ova this is delayed well beyond an hour during 

 which the polar bodies are extruded. When the membrane forms it 



