STUDIES OF FERTILIZATION. 3 



ripe gametes wherever found, franciscanns at this station and 

 elsewhere, with one exception, had relatively undeveloped gonads, 

 which, however, always contained ripe gametes, often in con- 

 siderable abundance, which fertilized readily. At the exceptional 

 station, well within Monterey Bay, all individuals of both species 

 had perfectly developed gonads. The waiter wishes to express 

 his appreciation of the hospitality of the Hopkins Marine Sta- 

 tion during this investigation, and his thanks to the Director, Dr. 

 W. K. Fisher, for his aid in securing material and in many other 

 essential ways. 



II. COMPARISON OF GAMETES. 



6\ franciscanns is much larger than 5\ purpuratus, commonly 

 almost twice the diameter, and its much larger spines cause the 

 impression of an even greater discrepancy in size. It is an in- 

 teresting fact that the gametes of the larger species are almost 

 correspondingly larger than those of the smaller, both in the case 

 of the ova and also the spermatozoa. The eggs of franciscanns 

 are no to 114 /JL in diameter, the eggs of purpuratus from 75 to* 

 79 fj.. The head of the spermatozoon of franciscanus is about 

 7ju, long by 2/x broad at the base, that of purpuratus is about 4 by 

 2 p. The jelly surrounding the franciscanns egg is about 30^ in 

 thickness and relatively firm and resistant, that surrounding the 

 egg of pnrpuratns is about 15/1 in thickness, relatively soft and 

 easily lost. 



III. CROSS-FERTILIZATION. 

 i. General. 



Loeb's recorded observations contain the only information in 

 the literature on the subject of the cross-fertilization of these two 

 species. They are to the following effect: (i) " If we mix eggs 

 of franciscanns and purpuratus in sea-water and add the sperm of 

 purpuratus the eggs of purpuratus will be fertilized more quickly 

 than the eggs of franciscanus; and the reverse is true if the sperm 

 of franciscanus is added to a mixture of both eggs in sea-water ' 

 (p. 273, Am. Nat., 1915). (2) "The sperm of purpuratus 

 shows no trace of cluster formation with the egg-sea water of 

 franciscanus, and yet the eggs of franciscanus are readily fertil- 



