68 ANIMAL AGGREGATIONS 



other males, and one female may become the center of a struggling 

 mass. One such group which Banta caught had 6 males fastened 

 together about a single female and 5 others nearby but not yet at- 

 tached. The actual egg-laying and fertilization of the eggs is ac- 

 companied by the formation of a close aggregation (Fischer-Sigwart, 

 1897). In addition to the male that has been in copulo for some time, 

 these supernumerary males gather and, despite kicks from the first 

 male, still manage to form a close clump. In Rana fusca one may 

 find single pairs, but as a rule fertilization is a community matter. 

 Supernumerary males also crawl over and among the egg masses and 

 effect the fertilization of ova which may not have been reached by 

 spermatozoa at the time of their discharge. 



At the close of the breeding season frogs scatter and resume a 

 solitary, non-social existence. 



Fish. — Similar breeding clusters of fish have been described by 

 Reeves (1907) with many identical details. With the rainbow darter 

 supernumerary males crowd about the spawning pair and appear 

 also to shed spermatozoa. Reighard (1903) has seen such behavior; 

 but in the main his studies (1903, 191 5, 1920) emphasize the orderly 

 spacing of breeding holdings in lish, a phase of the aggregation 

 phenomenon with which the present summary is not greatly con- 

 cerned. The close contact between males and females of fresh-water 

 animals with external fertilization is made necessary by the extreme- 

 ly short life of the gametes shed into fresh water. Reighard has 

 stated that fish sperm can remain functional for less than a minute 

 under these conditions. 



Snakes. — Snakes are reported to form bunches in the breeding 

 season similar to those described for frogs, except that they occur out 

 of the water (Ditmars, 1907; Ellicott, 1880; Ruthven, 1908). EUi- 

 cott records: ''I first saw such a bunch of snakes on the stony banks 

 of the Patapsco River, heaped together on a rock and between big 

 stones. It was a warm and sunny location where a human being 

 could scarcely disturb them. I reasoned that the warmth and the 

 quiet of that secluded space had brought them together. Some hun- 

 dreds could be counted, and all in a very lively state of humor, 

 hissing at me with threatening glances and with such persistency 



