STUDIES OF FEinn.lZATION 



531 



B. ARBACIA 



Tlie tests ooncorninp; tho rohition of the activity of spermatozoa 

 of Arbac'ia to the eheniical ooini)ositiou of the sea-water were not 

 so extensive as in the case of Nereis. Aloreox'er we do not liave 

 any definite ag'sre<2;ation I'c^iction liei'e to serve as a nuvasnn^ of 

 activity. However, a sufficient nunil^er of tests were made to 

 show tliat Arlmcia is much less sensitive to variations in inorganic 

 constituents tlian Nei-eis. 



COo. To afford c()mi)ai'isons we may use three forms here, 

 ( 'haetopterus, Arhacia and Nereis: 



100% CO2 



40% CO2 



20% CO2 



10% CO2 



5% CO2 



active 



paralyzed 

 paralyzed 



(^hactoptcrus. . paralyzed ! few move many iiuive active 



I slightly 



Arbacia paralyzed 1 paralj'zed j)aralysed paralyzed 



Nereis j paralyzed : paralyzed paralyzed paralyzed 



2.5% CDs 1% CO2 0.5% CO2 NORMAL SEA-WATER 



Chaetopterus active active active active 



Arbacia traces of fairh' active maximum a<'tivity 



movement active 



Nereis paralyzed paralyzed fair!}- maximum activity (ag- 



active gregation) 



Titus, while compared to Chaetopterus, Arbacia, is extremely 

 sensitive to the presence of CO2, compared to Nereis it is relati\'ely 

 insensitive. 



To other acids, H.SO., HCl, HNO„ and CH.-, COOH, Arbacia 

 is also less sensitive than Nereis, exhibiting a fair degree of activ- 

 ity in N/1000 solutions in sea-water (compare table for Nereis, 

 p. 526). 



The sensitiveness to alkalis does not differ materiallj^ from that 

 of Nereis. Agglutination of the spermatozoa is caused by N/2500 

 KOH, gi\'ing a \ery pretty precipitation picture in a vial. Such 

 agglutinations are irre\'ersible. Spermatozoa between the agglu- 

 tinated masses may be in motion. 



The relatixely slight sensitiveness of Arbacia sperm to CO2 is 

 correlated with absence of any such striking aggregation effects 



THE JOURNAL OF KXPEKIMENTAI. ZOOLOGY, VOL. 14, NO. 4 



