82 The Bullfrog, Rana catesheiana Shaiv. 



never could understand it, but the egg-laying of the species explains 

 the former puzzle. Frequently the bullfrogs laid their films in mid- 

 pond around stumps, or as we found in one instance they attached the 

 surface egg-film to the tips of some dead elderberry stems reaching 8 feet 

 out into the water. The western winds when strong create waves on 

 the water's surface and tend to break these original disks into smaller 

 ones, several of which we found. This reminds one of the same phe- 

 nomenon in green-frog complements. After this discovery, we skirted 

 the east edge of the lake and there found numerous small packets of 

 eggs or single eggs interspersed with the algae of the surface. The 

 eggs had drifted with the wind and in their present place were only 

 discovered because of the foamy air-bubbles. At this east edge they 

 hatch, and hence the reason for the tadpoles in this locality in prefer- 

 ence to their usual transforming sites, namely, the shallows. 



THE EGGS. 



Usually the record of the egg-masses was among brush or similar cover. 

 The disc form (Plate vii, Fig. 3), so prevalent in the green-frog, was 

 recorded in 14 cases. In one instance it covered a space of 2 by 2| feet 

 or 5 square feet ; in a second case, 2 by 2 feet ; and in a third, 2 by 1| feet. 

 The size of these masses is sufficient for identification, for a green-frog 

 egg-disc covering a square foot is very unusual. The first of these three 

 films was deposited upon a mass of driftwood and brush which was at 

 the surface; the second was found among some fresh white pine {Pinus 

 st7-ohus) branches that extended into the water from the edge of the 

 pond. One of the string-like masses previously mentioned was attached 

 to the roots of an overturned stump in shallow water, while another 

 was in brush beneath a boat-house float. 



The mass is glutinous and lacks the consistency of the Rana sylvatica, 

 pipiens, and palustris egg-masses, which are laid much earlier in the 

 season. 



In the last of June and through July only one other Rana is breeding, 

 namely, Rana clamata. One difference is, that the green-frogs have a 

 preference for vegetation. They lay on or among grass, water-plants, 

 and algse, or along grassy edges of ponds, while the bullfrog almost 

 invariably lays in brush (Plate xx, Fig. 1). The egg-complements of 

 the two species are also different: in the green-frog it seldom reaches 

 more than 3,500 to 4,000, while in the bullfrog it may be from 10,000 

 to 20,000. 



The egg has a black animal pole and a white or creamy white vegeta- 

 tive pole. If there be any semblance to an individual envelope, it 

 is from 6.4 to 10.4 mm. in diameter, but ordinarily it is so merged into 

 the loose mass that its identity would not be noticed unless especially 

 sought; its average is 7.6 mm., its mode 7.4 mm. The vitellus ranges 

 from 1.2 to 1.4 mm., rarely 1.1 mm.; its average is 1.3 mm., its mode 

 1.2 mm. The best character of distinction between the eggs of Rana 



