CRUSTACEA AS FOOD FOR YOUNG PISH. 



13 



Fig. 8. — Mysis ; " shrimp." Mysia reUcta. 

 After Ward and Whipple. 



Enlarged twice. 



The largest adult observed by Embody measured 11.47 mm. (about 

 0.45 inch). The average size of 31 egg-producing females was 8.05 

 plus mm. (about 0.31 inch). The smallest egg-producing female was 

 6.6 mm. (about 0.22 inch), and it was 497 days old and produced 

 25 eggs. The reproduction period for the species embraced the 

 months from January 8 to November 3, a period of 299 days, during 

 which time the range in temperature was from a minimum of 6° 

 to a maximum of 30° C. (42.8° to 86° F.). Eight days constituted 

 the period from oviposition to hatching, average temperature for the 

 time being 23° C. (73.4° F.). The calculated progeny from one pair, 

 producing an average of 45 eggs at one time, breeding approximately 

 19 times, is 855 in 

 299 days. A sec- 

 ond generation is 

 not produced in 

 the same breeding 

 season. The 

 young are carried 

 in the brood sack 

 on an average of 

 4 days, and in 

 180 days from 

 hatching grow 

 from 1.27 mm. to 

 3.57 mm. (0.05 

 to about 0.14 

 inch). 



In this connection it would seem worth while to refer to a species of 

 Eucrangonyx described as new by Embody in 1910. He called it 

 Eucrangonyx serratus and stated that the type specimens were col- 

 lected in March, 1908, from marginal vegetation of a " railroad 

 pond," in Virginia, about \\ miles north of Ashland. They were 

 said to be especially abundant in the thickest patches of sphagnum 

 and Utricularia at depths varying from a few inches to 1^ feet. 

 Associated with them were large numbers of Eucrangonyx gracilis 

 and Hyalella knickerhockeri. The pond in which they lived in such 

 great abundance was described as having an area of about 30 acres 

 and was said to be fed by springs within the pond itself and by a 

 small brook at the end. It was found that the fish of the pond fed 

 upon the amphipods liberally. The fish were largemouth black 

 bass {Micropterus salmoides), common sunfish {Lepomis gibhosus), 

 and calico bass {Pomoxis sparoides). The sunfish and calico bass, 

 1 to 3 inches long, some of which were able to penetrate the thick 

 masses of sphagnum which harbored the amphipods in great num- 

 bers, were observed to be relatively the greatest amphipod devourers. 

 This dense fringe of vegetation about the pond at all seasons, to- 

 gether with the rather large productiA^e capacity of the species in 

 question, prevented any very serious reduction of the numbers of 

 crustaceans. 



MYSIDACEA. 



Very few Mysidacea are known from the fresh water, and the only 

 species known in North America is Mysis relicta, which is considered 

 identical with a species living in lakes in northern Europe (Ireland, 



