ABT. 15 COPEPOD CBUSTACEANS OF CHESAPEAKE BAY WILSON 15 



docalanus, and the new species of Rohertsonia. For the July period 

 females of the two Acartia species again appeared bearing eggs, to- 

 gether with Oncaea venusta, Oithona brevicornis and O. simUis, 

 Microthalestris, Pseudodiaptomus, and the new species of Ganuella. 

 During the October period eggs were found upon females of Pseitr 

 dodia'ptomus^ Oithona siniilis, Harpacticus gracilis^ Ectinosoma cur- 

 ticorne, Lahidocera aestiva, Temora turhinata, and the two species of 

 Centropages. 



Other evidence of these four breeding periods was found in the 

 large number of development forms, nauplii, metanauplii, and 

 Cyclops stages, captured with the adults during the month following 

 each period. These development stages in the tow proved that the 

 eggs hatched a short time previously. 



The breeding periods caused rhythmic fluctuations in the total 

 numbers of specimens captured in the tow. It has already been 

 noted that the four largest hauls were made in March. It may now 

 be added that all the hauls made during that month had excep- 

 tionally high totals of specimens, although the hauls themselves were 

 few in number. This may be designated as the first, or spring, 

 maximum, and was the result of the January breeding season com- 

 bined with certain favorable conditions. Chief among the latter 

 may have been the relative scarcity of the fishes and other animals 

 that prey upon the copepods. The four largest hauls, those of Sta- 

 tions S, T, V, and Z, were made up practically entirely of the two 

 Acartia species. The fish that feeds most upon these copepods is 

 probably the shad, and as soon as it becomes numerous in the bay 

 during spring the copepods probably diminish rapidly. Ten differ- 

 ent stations in the bay were visited during March, and the average 

 number of specimens obtained at each of them was 36,500. Eight 

 of the same stations visited in June yielded an average number of 

 specimens of only 1,150, or less than a thirtieth as much. 



Thus the spring maximum was followed by a long decline, which 

 was only slightly modified by the April breeding season, and which 

 reached its lowest point, the year's minimum, in June. The July 

 breeding season brought the number of specimens rapidly up again, 

 and it was still further increased during the October breeding period. 

 The records give the following statistics: During January, 29 sta- 

 tions showed a total of 120,200 specimens, an average of 4,145. 

 During March, 10 stations gave a total of 365,200, an average 

 of 36,520. Two stations in April gave a total of 5,175, an average of 

 2,587. The total of 8 stations in May was 30,150, an average of 3,769. 

 In June, 13 stations yielded a total of 14,900, an average of 1,146. 

 Twenty-nine stations in July gave a total of 75,400, an average of 

 2,600. In August, 97,350 specimens were taken at 29 stations, an 



