440 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 



regular in the time for depositing their eggs, which is from 5 to 6 A. M. 

 During the two .summers that I studied Turritopsis at the seashore, 

 great numbers were collected and kept in aquaria. On many occasions 

 I arose early in the morning to observe the act of spawning, one 

 time they were watched through the entire night, and always the 

 act of egg laying was seen to commence at about 5 o'clock or a few 

 minutes after. Very rarely did it take place as late as 6 o'clock; and 

 on no occasion was the phenomenon observed more than a few minutes 

 before 5 A. M. 



This precise periodicity is not confined to Turritopsis, but seems- 

 to be very prevalent among the medusae in general. In Stomotnca 

 apicata, Stomotoca rugosa, and a species of Eucheilota, I find that the 

 eggs are deposited also at a fixed hour, namely, 5 to 5.30 A. M. Pro- 

 fessor Brooks found that Liriope and Eutima spawn at about 8 P. M. 

 In Gonionema Perkins found the time to be from 7 to 8 P. u. Bunting 

 found the period of dehiscence for Hydractinia to be at about 10 P. M. 

 Merejkowsky says that the eggs of Obelia are laid early in the morning. 

 Metschnikoff also gives the time of spawning of 14 species. 



Regular breeding habits have also been found to exist among other 

 marine animals, and may be more general than has been suspected. 

 Wilson, in his work on the development of Renilla, found that the eggs 

 of that form were always laid at about 6 A. M. In a single case only, 

 he says, the spawning took place as early as 5.30 and it was never 

 observed to occur later than 7 o'clock. The pelagic crustacean 

 Lucifer, Professor Brooks observed to deposit its eggs at from 9 to 

 10 P. M. 



Bunting found that by packing Hydractinia in ice and keeping it 

 at a lower temperature she was able to delay the time of egg laying. 

 On restoring the animals to the normal temperature, the eggs were 

 laid after a short period of time. Perkins found that the periodicity 

 of spawning in Gonionema is definitely affected by changes in light. 

 By placing his medusae in a dark place for an hour and then putting 

 them in the daylight, apparently normal egg laying again took place. 



While I did not try experiments on Turritopsis with regard to either 

 temperature or light, yet the changes of temperature from day to day 

 had no noticeable effect on the time at which they discharged their 

 eggs, that is, it occurred at the same hour on warm days and cool days. 

 In like manner the fact that the aquarium in which the medusae were 

 contained, was kept before a lighted lamp all night had no effect on 



