Oit. 2, 1879J 



NATURE 



5S9 



Thus the " rattle " of the poisonous rattlesnake (like the 

 expanding hood of the poisonous cobra) must tend to act 

 as a warning to creatures exposed to its attack. It is very 

 difficult to see what service this rattling can do to the 

 rattlesnake itself. It has indeed been suggested that the 

 sound resembles running water, and that in this way 



T.all of X^aulcsnake. 



creatures may be attracted to ils vicinity. I must say 

 that I for my own part have never been able to detect any 

 such resemblance. Moreover, to have such an effect the 

 rattling should be long-continued, whereas it is, in fact, 

 kept up but for a short time, and is only produced at com- 

 paratively rare intervals. 



Fig. 7.— Backbone of the Frog 

 (ventral a&pecl). 



Fic, 8.— Backbone oF the Frog 

 (dorsal aspect). 



Below the great group of reptiles is another group of 

 animals, at one time associated with them, but now recog- 

 nised as having a greater affinity with fishes. The group 

 of animals I refer to is that which is made up of frogs 

 and toads, together with efts (or newts), which latter are I 



such familiar objects in our ponds in the spring of the 

 year. 



The efts have all long tails, but the frogs and toads are 

 fully as destitute of a tail as we ourselves are, though 

 they have a long slender bone at the hind end of their 

 vertebral column, which bone reminds us of the plough- 

 share-shaped bone of birds. But you may recollect that 

 this tail-less condition, even in ourselves, does not obtain 

 in the very earliest stage of the human body. In frogs 

 and toads a "tailed" condition endures much longer j 

 for these animals, as you know, pass the first part of their 

 life entirely in the water as " tadpoles," swimming about 

 entirely by the undulating action of their long "tails." 

 The tadpole is at first a singular object. It consists of 

 a head and body indistinguishably united in one rounded 

 ball, from behind which a long and slender tail projects. 

 The creature may be said to be indeed at first " all head 

 and tail," for its head is relatively very large, and the 

 heart and other organsjmay almost be said to be included 

 within it. 



Fig. 9.— Tadpoles in dilTerenl slagcs of Jovelopmcnt, from those just hatcbcJ 

 (<; till the adult form is attained (8). 



Whatever may be the best way, however, of regarding 

 its head, there can be no doubt about its tail, its function, 

 or its fate. It is, as I have said, a swimming-organ, but 

 you know that as the tadpole becomes a frog or toad, it 

 either comes on land or swims in quite another fashion 

 from what it does as a tadpole, usually by striking out 

 with its legs and feet, just as we swim, only it does it 

 much better. Thus the tail becomes a superfluous 

 appendage, and indeed as the limbs grow, the tail is 

 gradually absorbed. It is not cast away ! Our popular 

 novelist was wrong in writing " What next ! as the tad- 

 pole said when his tail dropped off;" it does not "drop 

 off," but is sucked up by the creature's body gradually. 

 Indeed the animal feeds upon its tail, not by turning 

 round, biting, and eating it, but by its substance being 

 gradually taken up and absorbed by the blood-vessels, and 

 carried elsewhere, to assist the processes of bodily growth 

 and development which arc rapidly taking place. 



Tadpoles and efts lead us naturally to the last and 

 lowest class of backboned creatures the class of Fishes. 



