No. 614] 



PHYSIOLOGICAL PROBLEMS 



145 



from the middle of June to November. Miss Katherine 

 Norcross arranged the records in seasonal order, except 

 those of the spiders. In the case of the insects which 

 made up the vast majority of species on such an area, the 

 question constantly arose as to where the insect had been 

 previous to its appearance there. During the spring and 

 summer of 1913, the writer undertook to collect and ob- 

 serve the spiders of the plot studied by Allen. Spiders 

 were selected for this study because they do not undergo 

 a metamorphosis, and may often be found and identified 

 in a juvenile condition while insects can not. Though in- 

 complete, the data are adequate for a discussion of the 

 physiological features of seasonal succession. 



The habitat from which the specimens were collected 

 was about 25 X 50 ft., nearly all of it covered with water 

 in early spring, usually drying during May, and contain- 

 ing water thereafter only during and after especially 

 heavy rains. In July Allen found the vegetation com- 

 posed chiefly of Eleocharis, Spartina, Carex, Juncus, Lia- 

 tris, Steironema, Caealia, and several other composites. 

 The plants taken together made up what is commonly 

 called coarse grass and weeds. The writer's collections 

 in 1913 were made on or very near Allen's dates for 1910. 

 From these joint sources the data of the following table 

 were obtained and arranged, but with some gaps where 

 the spiders were probably too young to identify. The 

 records marked "C" are taken from Comstock ('11) and 

 represent the conditions in which the spiders usually are 

 at the dates indicated. The spiders were identified by 

 Banks ( '10) and the nomenclature is according to his list. 



1. Statement of Succession.— In the spring the area is 

 a pond in which various Crustacea and worms succeed 

 each other (see Shelf ord, '13, pp. 278). Sexually mature 

 adults appeared in abundance about as follows : Ambly- 

 stoma tigrinum, March 15 ; Eubranchipus, April 15 ; Pla- 

 naria velata, May 1 ; Diaptomus stagnalis, May 1. Some 

 of these animals have been studied sufficiently to show 

 that they become dormant for the remainder of the year 



