Dkcbmbbk 26, 1902.] 



SCIENCE. 



1037 



Agitation seems, in some way, associated 

 with hatching. Eggs of many species, after 

 remaining upon the surface of water, or 

 upon the bottom of breeding vessels for days, 

 hatch if removed to a phial and shaken, but 

 if left undisturbed, will remain unhatched 

 for months (in the case of Conchyliates musi- 

 cus, shaking eggs is a favorite way of forcing 

 a hatch). Eggs under similar conditions will 

 hatch if placed in a one per cent, or two per 

 cent, solution of formalin. To determine, 

 under natural conditions, the influence of agi- 

 tation upon hatching, careful observations 

 were made during the past summer where the 

 water in mosquito pools evaporated and the 

 ponds remained dry for months. As soon as 

 sufficient rain fell, and the disturbances of 

 trickling water were present, larvae of Con- 

 chyliates musicus, Psorophora ciliata, Psor- 

 ophora howardii, and a few species of Gulex, 

 could be found in the pools a few hours after 

 the rain. This led to the conclusion of a 

 very great irregularity in hatching, and to 

 the belief that the species of Psorophora are 

 single-brooded in Louisiana. The eggs of one 

 season hatch irregularly the next. The major- 

 ity, however, hatch in June, July and August 

 when rainfall is sufficient. Hatchings may 

 occur as late as November, but at this 

 time larvse are scarce. Conchyliates musicus 

 is equally irregular in hatching, though more 

 than one brood a year prevails. We have un- 

 hatched eggs of C. musicus at the time 

 of this writing that were deposited in July. 

 That they are fertile has been proved by 

 taking some of the same brood at different 

 intervals and forcing a hatch by agitation. 

 Eggs of Psorophora ciliata and P. howardii 

 deposited in July and August have failed to 

 hatch under such treatment, but the single- 

 brood theory may account for the resistance 

 of the eggs of this genus. 



Dr. John B. Smith's conclusions upon the 

 egg-laying habits of Culex sollicitans, that of 

 depositing upon marsh grass, certainly must 

 be considered as exceptional, as also his ob- 

 servation of dark (black) eggs in the bodies 

 of dissected specimens. In not a single in- 

 stance, sollicitans included, have we observed 

 a form to deposit dark eggs, nor have we found 



any to oviposit upon anything but water. Eggs 

 floating about become attached to floating 

 debris just as they do to the sides of vessels 

 in which the water has been allowed to evap- 

 orate. Injured specimens will make desperate 

 efforts to reach vessels of water to oviposit, 

 but failing to do so, refuse to lay. We have 

 not found a single species to deposit eggs 

 without water, save a few specimens subjected 

 to the abnormal conditions of mounting for 

 the cabinet, or for study. 



From our studies we draw the following 

 conclusions : 



1. That boat-shaped masses of eggs are 

 not general. 



2. That eggs of most species sink when 

 slightly agitated. Even the eggs of Culex 

 pipiens will sinli (and hatch) when separated 

 and shaken. 



3. That the hatching of the eggs of many 

 species is not at all regular. Pools upon 

 which eggs are laid may dry up and remain so 

 for months, and the fertility of the eggs is in 

 no way impaired. With Psorophora, the eggs 

 of one season hatch the next; while with 

 Conchyliates musicus, and with many species 

 of Culex, eggs laid in the fall remain un- 

 hatched all winter. Thus many of our spe- 

 cies hibernate in the egg condition. (Eggs of 

 Stegomyia fasciata, left high and dry by evap- 

 oration, have remained unhatched sixty-one 

 days, and when moistened and agitated, soon 

 hatched.) 



4. That the period of larval life may be 

 greatly prolonged by insufficient food and low 

 temperature, and that pupal and adult stages 

 are very much longer late in the season than in 

 midsummer. It is possible for a few adults 

 to hibernate, even of the same species as the 

 hibernating eggs. 



5. That it is exceptional for mosquitoes, 

 including Culex sollicitans, to deposit eggs 

 upon substances other than water. 



6. That it is exceptional for black eggs to be 

 deposited, or for mosquitoes to use their hind 

 legs during egg deposition. 



Y. That the common breeding places of mos- 

 quitoes are transient pools (due as much to 

 the enemies in permanent pools and waterways 

 as anything else), in consequence of which 



