308 BULLETIN OF THE BUREAU OF FISHERIES 



yielded a great abundance of Evadne off Gloucester, 1 to 10 miles out in Massachu- 

 setts Bay. It was less abundant 16 miles out and scarce or absent over the northern 

 end of Stellwagen Bank. A tow made that same day close to the extremity of 

 Cape Ann yielded only a fraction as many Evadne as off the mouth of Gloucester 

 Harbor, and only a scattering was taken two days later in Provincetown Harbor, 

 though young herring seined there were full of Podon and Evadne. 



In the North Sea region Evadne is definitely seasonal in its occurrence. The 

 two species whose occurrence there has been plotted — spinifera and nordmani — are 

 both most plentiful in August. The entire stock of the former produces resting 

 spores in autumn; then dies off. This is likewise the fate of most of the nordmani, 

 though some few of these survive and continue to reproduce parthogenetically dur- 

 ing the winter. The spores of the two species winter on the bottom, hatch in May, 

 and by rapid asexual multiplication the stocks are again built up to their summer 

 plurimum. 61 



Specific identification of the Evadne of the Gulf of Maine has not been attempted 

 as yet, but our few records of the genus as a whole, with McMurrich's data for 

 Podon and Evadne at St. Andrews, show a corresponding seasonal periodicity in 

 the Gulf of Maine, all falling within the period June 8 to September 20, with the 

 largest offshore catches in August and September. At Woods Hole, Fish (1925) 

 found Evadne nordmani most plentiful in November, least so in spring, but E. ter- 

 gestina at its maximum during the summer and early autumn. 



Cladocera are one of the most important items in the diet of many species of 

 larval and post-larval fishes in British waters (Lebour 1919 and 1920). Judging 

 from the general similarity between the planktonic communities in general, proba- 

 bly this applies also to the inshore waters of the Gulf of Maine. The various young 

 fishes that are in shoal water there in summer will probably be found to consume 

 Evadne and Podon regularly — -herring, for instance, as just noted. 



WORMS 



Glass worms (ch^tognaths) 62 



Four species of chsetognaths are known from the Gulf of Maine, one of which — 

 Sagitta elegans — is a regular member of the local endemic plankton while the others 

 enter its limits as immigrants only. 



Sagitta elegans 



If I were asked to name three animals as most characteristic of the plankton 

 of the offshore waters of the Gulf of Maine I should unhesitatingly select the 

 copepods Calanits JinmarcTiicus and Pseudocalanus elongatus and the chsetognath 

 Sagitta elegans. m Throughout the year and in every part of the Gulf of Maine, as 

 well as over the offshore banks which inclose it on the south, this large, active, and 

 voracious worm is so nearly universal that it has been taken at practically every 

 station and in the great majority of our hauls. To the east and north of our limits, 



»> See Apstein (1910) lor an account of the seasonal cycle. 

 •'Identifications follow von Ritter-Zahony (1911) and Huntsman (1919). 



83 1 follow Huntsman (1919) in treating as a unit the soveral "subspecies" of S. elegans, a species comparable to the herring, 

 among fishes, in Its tendency to develop local races in different physical environments. 



