NO.1302. AMERICAN PARASITIC ARGVLIDzE—WILSOX. 661 



gan, began to hatch on the 25th, a period of only eighteon days. And 

 yet, from actual tests, the temperature of tlie atiuai'ium did not rise 

 above 65" F. during that time. 



For ^l. inegalops the time is much longer; the eggs obtained from 

 Woods Hole were laid October 80 and 31; the}" did not begin to hatch 

 until December 12, and the larvai had not all emerged before Decem- 

 ber 80 (sixty days), nearly double the time required for the two first 

 species. And there is another consideration which makes this dis- 

 parit}^ even greater than it seems at first sight. No statement of 

 the conditions under which developn]ent took place is made by any of 

 the authors save Kellicott (1880). Dana and Herrick, however, do 

 mention (1837) that the female of A. catostoini laid her eggs upon the 

 sides of the aquarium, and it is to be presumed that thev remained 

 there until hatched. Probably also the times recorded by the other 

 authors were obtained from eggs kept in aquaria. 



Such at least is the case with the eggs of ])oth catostomi and )neg<ilops 

 observed by the present author. And in both instances the water of 

 the aquarium stood at about the same temperature (72° F.) as that of 

 the room in which it was kept. 



This would not be much of a change from their normal environ- 

 ment for the eggs of catostomi^ for they were not laid till May 14, 

 and were kept through June into July, hatching from June 11 to 20. 

 The temperature of the water in the pond from which the females 

 were taken must have risen during that time to within a comparatively 

 few degrees of the room mentioned. But in the case of A. megalop^ 

 there was a radical diflerence in the environment; these eggs were 

 taken from the open ocean on October 80, and kept through November 

 and into the latter part of December. Hence a temperature of 75° 

 would be at least 30° or 35° higher than that of the salt water at 

 Woods Hole during those months. This would mean, of course, that 

 the eggs developed much faster than in their normal surroundings, so 

 that we must add eight or ten days to the period just given ])efore 

 comparing it with the other species. 



Hence incubation is fulh' twice as long in meyalops as in foliaceus 

 or catostomi. But even this record is surpassed by that of A. disos- 

 tethii. Kellicott records (1880) that the eggs laid in his aquarium on 

 August 28 did not show the dark eye dots until October 5, and did not 

 begin to hatch till November 17, a period of eighty-one days! Here the 

 author distinctly states that the tank was kept at the temperature of 

 the room, and hence something would need to be added to even such an 

 enormous period as this before it would fairly represent the length of 

 incubation under normal conditions. It is also stated that these eggs 

 were kept out of the light, and Kellicott thinks that this influenced the 

 incubation. Possibl}^ it might otfset the increase in temperature, but 

 we must remember that in depositing her eggs under normal condi- 

 tions the female Argulus must needs often get them in the shade. It 



