12 



NA TURE 



{Nov. 6, 1873 



poison-organs are probably only used for defence. They 



are formed, however, on the very same type as are the 

 poison fan;j5 of vipers. Unlike the latter, however, they 

 are not modified teeth, nor are they situated within the 

 mouth as they always are in poisonous serpents. 



A Fro» ' helohaUs fuscus) which is common in France 

 (and which is interesting on account of the form of its 

 skull hereafter to be pointed out,, though really harmless 

 enough, has a singular power of making itself offensive. 



Both m^iles and females of this species utter a kind of 

 croak, and both, if their thigh is pinched, produce a 

 sound like the mewing of a cat. At the same time they 

 emit a strong odour, which is like that of garlic, and be- 

 comes stronger as the animals are more disturbed. This 

 emission not only affects the sense of smell, but even 

 makes the eyes water as mustard or horseradish does. 



This singular power, together with the acrid secretion 

 of the toad, are the nearest approximation to venomous 

 properties possessed by any members of the order, no 

 toad — not even the giant of the order Bii/o agua — being 

 real'y poisonous. 



A small Frog, by no means uncommon in France and 

 Germany 'Alyles obsUtricans) has a very singular habit. 

 The female lays its eggs 'about sixty in number) in a long 

 chain, the ova adhering successively to one another by 

 their tenacious investment. The male twines this long 

 chaplet round his thighs, so that he acquires the appear- 

 ance of a courtier of the time of James 1. arrayed in 

 trunk hose or puffed breeches. Thus encumbered, he 

 retires into some burrow 'at least during the day; till the 

 period when the young are ripe for quitting the egg 

 Then he seeks water, into which he has not plunged many 

 minutes when the young burst forth and swim away, and 

 he, having disencumbered himself of the remains of the 

 ova, resumes his normal appearance 



Certain Frogs forming a very large group) are termed 

 Tree-frogs, from their adaptation to arboreal life by m£ans 

 of the dilatation of the ends of the digits into sucking discs, 

 by which they can adhere to leaves. One of them, the 

 common green Tree-frog {Hyla arbored) is spread over 

 f^urope, Asia, and Africa, in the same manner as R. escu- 

 Unta, except that it is not found in the British Isles. A 

 few toads also have the tips of their digits similarly di- 

 lated. Such, e.g., is the case in the '/^eaera. Kaloula of 

 India, and Bracliymerus of South Africa. 



The female of a peculiar American Tree-frog {Noto- 

 trema marsupialum) has a pouch extending over the whole 

 of the back and opening posteriorly. Into this the eggs 

 are introduced for shelter and protection. A dorsal jX)uch 

 also exists in the allied American genus, Opisthodelphys. 

 An American species of Hy lodes has the habit of laying 

 its eggs in trees singly in the axils of leaves, and the only 

 water they can obtain is the drop or two which may from 

 time to time be there retained. 



A still more remarkable mode of protecting the egg is 

 developed by the Great Toad of tropical America (/'i)5<z 

 anuricatui). In this case the skin of the females' back at 

 the laying season thickens greatly and becomes of quite a 

 soft and loose texture. The male, as soon as the eggs are 

 laid, takes them and imbeds them in this thick, soft skin, 

 which closes over them. Each egg then undergoes its 

 process of development so enclosed, and the tadpole stage 

 is, in this animal, passed within the egg, so that the young 

 toads emerge from the dorsal cells of the mother com- 

 pletely developed miniatures of the adult. As many as 

 120 of these dorsal cells have been counted on the back 

 of a single individual. 



The only instance of a similar cutaneous modification 

 is that pointed out by Dr. Giinther * in the skin of the 

 belly of the Siluroid fish, Aspredo batrachus. Here he 

 found that " the whole lower surface of the belly, thorax, 

 throat, and even a portion of the pectoral fins, showed 



* See Catalogue of the fishes in the Biitish Muieum, vol. v. p. 36t. 



mimeroos shallow, roimd impressions, to which a part of 

 the ova still adhered." He concludes that " it is more 

 than probable that towards the spawning time the skin of 

 the lower parts becomes spongy, and that, after having 

 deposited the eggs, the female attaches them to it by 

 merely lying over them." " When the eggs are hatched 

 the excrescences disappear, and the skin of the belly be- 

 comes smooth as before. Even in the highest class of 

 animals {Mammalia j we are familiar, in the Kangaroo and 

 Opossum order ' Marsupialiaj, with a special external 

 receptacle (the marsupial pouch) for the protection and 

 secure development of the young ; but nothing of the 

 kind exists amongst birds or reptiles. In fishes, however, 

 the male of the litde Sea-horse 'Hippocampus) is pro- 

 vided with a ventral pouch in which the eggs are shel- 

 tered, and the same class presents tu with a mode of 

 carrying the eggs still more bizarre than that of AlyU: 

 obsUtricam just related. In the fish Ariw. fiuui the male 

 actually carries about the ova in the mouth, protected by 

 the jaws, till relieved of the inconvenience by the hatching 

 of the young fiy. 



A South African Toad (DactyUthra capsntis] is in- 

 teresting, as we shall hereafter see, on account of certain 

 anatomical points in which it agrees with Pipa, and 

 differs from all other Anoura. N'o interesting facts, how- 

 ever, are known as to its habits. 



Another noteworthy form is the Mexican Rkiru>phryn:i: 

 dor sails, the exceptional characters of which are tht: 

 tongue, which is free in front instead of behind, and the 

 enormous spur-like tarsal tubercle. 



Almost all Frogs and Toads pass the first stages of 

 their existence in water, going through a free, tadpole 

 stage, and a'l are more or less aquatic when adult. The 

 only exceptions are Pipa, Xototrema, Opisthodilpkys, 

 and the Hylodes before referred to. V'ery many kinds, 

 however, are, when adult, inhabitants of trees. The 

 question may suggest itself to some, ".A.re there any 

 which can be said in any sense to be aerial animals.'' 

 Birds are almost all capable of true flight, as also are 

 those aerial existing beasts the Bats, and as were those 

 extinct reptiles the Pterodactjles. Certain squirrels an i 

 opossums can take flitting jumps by means of an exten- 

 sion of the skin of the flank, arid a similar, though much 

 greater extension, supported by elongated freely ending 

 ribs, is found in the little lizards 'Draco) called Flying 

 Dragons. 



The class of Fishes supplies us, also, with an example 

 of aerial locomotion in the well-known Flying Fish. 



Since, then, every other class of vertebrate animals 

 (Beasts, Birds, Reptiles and Fishes) presents us with 

 more or fewer examples of the aerial species, we migh: 

 perhaps expect that the Frog-class would also exhibit 

 some forms fitted for progression through the air. We 

 cannot say with certainty that such is the case ; but Mr. 

 Alfred Wallace, in his travels in the Malay Archipelago, 

 encountered in Borneo a Tree-frog {Rhacophorus, to which 

 he considers the term " flying " may fairly be applied, and 

 of which he says, it "is the first instance known of a 

 flying-frog." Of this animal he gives us the following 

 account : — 



" One of the most curious and interesting creatures 

 which I met with in Borneo was a large tree-frog which 

 was brought me by one of the Chmese workmen. He 

 assured me that he had seen it come down, in a slanting 

 direction, from a high tree as if it flew. On examininc' 

 it I found the toes very long and fully webbed to their 

 extremity, so that, when expanded, they offered a surface 

 much larger than the body. The fore-legs were also 

 bordered by a membrane, and the body was capable of 

 considerable inflation. The back and limbs were of a 

 very deep shining green colour, the under surface and the 

 inner toes yellow, while the webs were black rayed with 

 yellow. The body was about four inches long, while 

 the webs of each hind foot, when fully expanded, covered 



