NATURAL HISTORY OF CUMIXiilA TKLLIXOIDKS. 217 



the presence of eggs they become greatly activated and again 

 swim vigorously. A very few are capable of becoming so acti- 

 vated up to the time when the life of the suspension becomes ex- 

 tinct, and a few fertilizations result, (i to 5 per cent.). 



It is interesting to note that J. Nelson observed that oyster 

 sperm in the presence of egg secretions would wear out their 

 limited store of energy within an hour and become incapable of 

 causing fertilization. 



I have not observed that spermatozoa in very dilute suspensions 

 quickly lose their power to fertilize eggs while still motile as 

 described by Professor Lillie for Nereis sperm, but it was observed 

 that in very dense suspensions spermatozoa retain their vitality 

 and ability to fertilize from two to three days. This phenomenon 

 has been observed also by Gemmil, Lillie and Cohen. Gemmil 

 ascribes it to the nutritive quality of the spermatic fluid, while 

 Lillie and Cohen show- that "it is due, at least in part, to the 

 inhibiting effect of CO 2 in solution or to hydrogen ion con- 

 centration." Of course this extreme condition is never met with 

 in nature. 



BEHAVIOR OF THE LARVA. 



The larva becomes ciliated as a late blastula and, as an early 

 gastrula it develops a strong prototroch and rises to the top. 

 It swims vigorously until the trochophore fully transforms to the 

 veliger. After becoming a typical veliger it soon settles to the 

 bottom temporarily and from that time on it swims less and 

 less frequently until it approaches the time of metamorphosis. 

 Late veligers rarely swim and the velum appears to become 

 more and more an accessory feeding organ. A certain amount 

 of feeble movement is maintained until metamorphosis is com- 

 pleted, and the velum disappears. The velum persists until the 

 form of the larva indicates that metamorphosis is practically 

 complete though it becomes less and less vigorous after the 

 first few days of active swimming. 



LUNAR PERIODICITY. 



As indicated by the foregoing statements Cumingia shows a 

 lunar rhythm in spawning. The period of the first quarter is 

 the period of restricted spawning and full moon until new moon 



