Febniary, i;)21. 



The Canadian Field-Naturalist. 



23 



The mouth-parts lose their former loco- 

 motoiy functions and become limited to 

 masticatory processes. The genital organs 

 begin to appear and the tail grows rapidly 

 in length, so tliat soon the shape of the 

 adult is reached, and only the particular 

 development of the claspers and the gen- 

 ital organs remain. The eggs of the fairy 

 shrimps apparently do not all hatch at the 

 same time (day). I have observed how nau- 

 plii and metanauplii or young and full- 

 grown individuals are present together in 

 the same pond, though the great majorit}' 

 of the individuals are either in one stage 

 or the other. 



The fairy-shrimps are of a transparent 

 reddish, j^ellowish, blueish or greenish 

 color, more pronounced on some parts 

 of the animal than on others. Besides, cer- 

 tain species, especially the females, have 

 additional strong purple, violet, brownish 

 or black colors in patterns characteristic 

 for each species, though there is great 

 variety in the intensity in the various indi- 

 viduals. In the males the most strongly 

 colored parts of the body are generally 

 the claspers (second pair of antennie) and 

 in the females the parts near the ovarium; 

 also the underside of the head, the foli- 

 aceous legs and the tip of the tail in both 

 sexes. The ripe eggs have a strongly yel- 

 low, orange or light brown color. 



The fairy-shrimps swim in the water with 

 equal facility upon the belly or upon the 

 back, according to whether their food is 

 above or below them in the water. Loco- 

 motion is accomplished by means of the 

 foliaceous legs and by the long tail serving 

 as a rudder; when disturbed they will 

 make a sudden jerk with the tail and dart 

 in one or the other direction. Where there 

 is a strong current in the pond (lake) in 

 which they live they will go with it though 

 moving their foliaceous legs all the time; 

 in quieter pools, the younger individuals es- 

 ]ieeially (metanauplii and slightly older 

 ones) will float in the water belly down- 

 wards with little apparent movement from 

 place to place, if left undisturbed. Their 

 food consists of smaller, aquatic inverte- 

 brates (Cladocera, etc.), and I have often 

 observed them "browsing" in the mud- 

 bottom of the pond or among the green 

 algae there. In return they form aji im- 

 portant item in the diet of certain aquatic 



insect larvie (beetles, caddis-flies, etc.) or 

 young fishes, against which they have lit- 

 tle other protection than their trans- 

 parency. Just prior to and during the 

 time the eggs are becoming ripe the fe- 

 males generally carry the males around; 

 the latter seize their mates around the 

 genital somites dorsally with their claspers 

 and retain their hold until the time of co- 

 pulation is over. Then the males leave 

 their "victim" for another female and 

 repeat the process, which is perhaps a ne- 

 cessary procedure as there are generally 

 far more females than males of a certain 

 species in the 'same pond. When the eggs 

 have been laid they, so far as has been ob- 

 served, rise to the surface of the water and 

 float there until hatched, or if the pond 

 dries up or freezes to the bottom they re- 

 main (hibernate) in the mud until hatch- 

 ing is possible, when the pond is again 

 filled with water or its ice melts. As a 

 matter of fact this desiccation or freezing 

 (hibernation) of the eggs seems to be ne- 

 cessary for their development (isee Ottawa 

 Naturalist, April, 1896, Prince). 



The sudden appearance of the fairy- 

 shrimps is truly wonderful and has long 

 puzzled students. Outside of the arctic 

 they are generally found only in temporary 

 pools or ponds, being hatched there in 

 thousands as soon as the ice in the latter 

 melts or when they are again filled with 

 water. In the arctic and probably in 

 mountain-lakes (ponds) at high elevation, 

 say about 10,000 feet, where the conditions 

 are similar, nauplii appear (hatch) im- 

 mediately after the ponds melt (June), 

 and the animals have thus a period of 3-4 

 months in which to grow to maturity and 

 deposit their eggs in case the pond they 

 are found in does not dry up before the 

 water freezes and all, except the hibernat- 

 ing eggs, are killed off by being frozen into 

 the ice, or die a natural death. At more 

 southern latitudes, however, and at lower 

 elevations, the ponds in which they occur 

 are far more likely to dry up ; thus near 

 Ottawa, Ontario, I have found the first 

 ones in the middle of April -, when they 

 (Euhranchipiis gelidus) were about 1 cm. 

 long, thus young individuals probablj" 

 hatched a couple of weeks before; the full- 



2 See also HaLkett's observatioji, Ottawa 



Naturalist, July, I'SSoJ p- 89..' 



-:i :\bl;>:;. 



