161 



AMPHIBIA. 



AMPHIBIA. 



163 



December, 1826, two of the toads were dead; the other two alive, but 

 greatly emaciated. 



Dr. Buckland concludes from the experiments generally, that toads 

 cannot live a year excluded totally from atmospheric air ; and from 

 the experiments made in the larger cells in the Oolite, that there is a 

 probability that those animals cannot survive two years entirely 

 excluded from food. (' Zoological Journal,' vol. v. p. 314.) 



Absorption of Air and Water, Exhalation, and Transpiration. A 

 rapid process of absorption and evaporation of fluids, by the pores of 

 the skin, gives to the Anourous Amphibia the power of resisting heat. 

 If a frog be plunged into water, of a temperature of 40 Centigrade 

 (104 Fahr.), it will not, it is asserted, live more than two minutes, 

 though the head be left out so as to enable it to respire freely ; yet a 

 frog will sustain the action of humid air heated to the same tempera- 

 ture, for four or five consecutive hours. A sudden transition, however, 

 from a low temperature to a high one, is generally speedily fatal to 

 these animals. Their proper balance of animal heat is kept up by a 

 regulation of the evaporation of liquid absorbed, or by the transpiration 

 of the matter, the quantity of which is augmented in proportion as 

 the external heat is more intense ; and the animal resists it as long 

 as the moisture is not desiccated by the air. When it can no longer 

 repair the loss of the moisture already taken up, by a fresh absorption 

 of liquid, it perishes. The Frogs, in this particular of their organisa- 

 tion, have been compared to the vessels which in Spain are called 

 Alcarazas, used for cooling water, by the transudation permitted by 

 their porous structure. Dr. Townson, who made observations to 

 some extent upon this subject, and had two frogs, which he named 

 Damon and Musidora, found that a frog would sometimes absorb in 

 half an hour as much as half its own weight in water, and, in a few 

 hours, nearly its entire weight. When the animal so filled was placed 

 in a warm and dry situation, it gave off this fluid nearly as rapidly as 

 it had accumulated it. He contends that the Frog Tribe never drink, 

 and general observation goes to prove that the Frogs, Tree-Frogs, and 

 Salamanders do not swallow liquids, being supplied by the process 

 before mentioned. The meagreness of some of these animals, in a 

 state of comparative desiccation, and their apparent plumpness after 

 they have renewed their supply of moisture, is very striking. If, 

 when so supplied, they are suddenly surprised, they can get rid of 

 their load instantaneously. Few who have come on a frog by surprise, 

 in a moist meadow, have not observed that, during its first leap, it 

 emits a quantity of liquid from its vent. " Whatever this fluid may 

 be," saya Dr. Townson, " it is as pure as distilled water and equally 

 tasteless. This I assert as well of that of the toad, which I have often 

 tasted, as that of frogs." This fluid is the liquid absorbed, by the 

 skin of the abdomen principally, and for which toads and frogs are 

 ever on the look-out The dew on the herbage is a frequent source 

 of this necessary supply, and in dry seasons toads will bury themselves 

 in moist sand or earth for the purpose of bucking up through their 

 gkin any aqueous particles which may be around them. The fluid 

 is contained in a sac, generally consisting of two lobes, situated in 

 the lower part of the abdomen under the viscera, and is conducted to 

 the receptacle by particular vessels, which are certainly not the ureters 

 or urinary canals from the kidneys : these urinary canals have their 

 exit lower down in the cloaca. Blumenbach, and even Cuvier, in his 

 ' Lecons 6? Anatomic Compare^,' considered this bilobated bag as 

 the urinary bladder in the frog and toad ; but Townson shows that it 

 has no connection with the ureter, which, as we have seen, has its 

 posterior opening lower down in the cloaca, while these receptacles 

 terminate in the front of that intestine. 



Brain, Nervous System, and Senses. The brain and nervous system 

 of the Anourous Amphibia are, as in the Reptiles generally, composed of 

 an encephalon consisting of a cerebrum, cerebellum, and medulla 

 oblongata ; a spinal cord ; and the nerves which are given off 

 from these sources to the different organs of the body. So far the 

 system is modelled upon that of Marnmiferous Animals and Birds, 

 but the cerebellum is proportionally much less. The Reptiles have 

 also a ganglionary nervous system, or a great double sympathetic 

 nerve. 



Touch. The naked skin and its sensibility to variations of tempe- 

 rature would seem to indicate a considerable degree of perception, as 

 to the physical and even chemical nature of the bodies with which it 

 comes in contact. But touch, properly so called, can hardly exist 

 in a high state of development in the greater part of the Anourous 

 'in. They have, indeed, no nails on their toes, which are much 

 longer in the frogs than in the toads ; and in many of the genera and 

 species the toes are terminated by fleshy appendages, as in Pipa, 

 which has also an elongated fleshy muzzle ; the Tree-Frogs (Ifyla) also, 

 have the extremities of their toes dilated into fleshy disks, which, like 

 the acetabula of the Sejiiada;, adhere by their circumference. These 

 enable the animals to walk in all directions upon flat surfaces, and to 

 adhere to them even when they are of the smoothest nature. The 

 MUM of touch is probably more highly developed where this organi- 

 Kiition is manifested. 



Taste. Probably not at all acute. The tongue, as we have seen, is 

 an organ for the capture of the prey, which is swallowed entire 

 t, in the same moment that it is taken. 



Smell. This sense would seem to be almost rudimentary in the 

 ,1 //>/! /'/,/. A simple opening pierced from the end of the muzzle to 



KAT. HIST. DIV. VOL. I 



the front of the palate, with a fleshy and concave membrane at its 

 external extremity, moving in unison with the respiratory action, is 

 strongly contrasted with the intricate and beautiful structure of the 

 nasal organs which are so highly developed in the Carnivorous 

 Mammalia and Birds. 



Hearing. There is a considerable difference in the structure of the 

 organ of hearing among the Anourous Amphibia. The Pipa, for 

 instance, has a sort of small valve upon the tympanum, somewhat 

 similar to that possessed by the crocodiles, and probably intended to 

 protect the membrane against the pressure of the water when the 

 animal resorts to great depths. Jlyla and Sana have the tympanum 

 distinctly manifested by the delicacy of its structure wheu compared 

 with the other integuments of the head. In the Toads the tym- 

 panum is not apparent. Examples of the structure of the ear may 

 be seen in some of the preparations in the museum of the College of 

 Surgeons. 



Sight. The precision with which a Toad measures the distance of 

 an insect, and captures it with its tongue the moment the victim is 

 within reach of that organ, shows a high and accurate development 

 of the organs of sight, as applicable to short distances at least. The 

 pupil is, in general, round, but in the Anourous Amphibia whose 

 habits are nocturnal (the toad, for instance) it is angular or linear. The 

 humours vary in their proportions in the different genera, but the 

 crystalline humour has been noticed of greater density and of a more 

 spherical figure in the aquatic species. The orbits are generally 

 incomplete, and sometimes protected, as in Ceratophrys, by folds of 

 thickened cuticle. 



Reproduction. The special reproductive tissues of the male in the 

 Anourous Amphibia are situated in the cavity of the abdomen below 

 the kidneys, and the deferent canals terminate in the cloaca. The 

 ovaries in the females are found in the same situation with the cor- 

 responding parts in the males, and are of considerable volume. Their 

 free extremity forms a sort of trumpet-shaped opening, and the oviduct 

 terminates in the cloaca, whence the eggs are excluded. Blumenbach 

 describes the Frogs of his country as having a large egg-cavity, divided 

 by an internal partition into two parts, from which two long convo- 

 luted oviducts arise, and terminate by open orifices at the sides of 

 the heart. The ovaria, he says, lie under the liver, so that it is 

 difficult to conceive how the eggs get into the above-mentioned 

 openings. The egg-cavity, he adds, opens into the cloaca. The Toads, 

 according to him, have not a large egg-cavity; but their oviducts 

 terminate by a common tube in the cloaca. 



At the season of reproduction, besides the vocal manifestations, 

 there are others which visibly distinguish the male in many of the 

 Amphibia. At each croak, the male Green Frogs project from the 

 commissure of the mouth two globular bladders into which the air is 

 introduced, and the throat swells and becomes coloured. In the males 

 of the Red Frog the thumbs of the anterior feet become considerably 

 swollen and covered by a black and rugose skin at this period. 

 The eggs are not fecundated until after they have been extruded into 

 the water. These eggs are enveloped in a sort of delicate, mucous, 

 permeable membrane ; they are, when excluded, most frequently 

 agglomerated either in glutinous masses or chaplets, and increase 

 considerably after they are plunged in the water. There are however 

 some curious modifications of the disposition of the eggs in certain 

 species of the Anourous Amphibia. In the Toad, called by Laurenti 

 from its habits Bufo obstetricans, the male, for instance, after the 

 exclusion of the eggs, takes up the chaplets, and disposes them round 

 his thighs, something in the form of a figure of 8. He is then 

 said to carry them about till the eyes of the embryo become visible. 

 At the proper period for hatching, he conveys his progeny to some 

 stagnant piece of water, and deposits them, when the eggs break and 

 the tadpoles come forth and swim about. The male Pipa, or Surinam 

 Toad, as soon as the eggs are laid, places them on the back of the 

 female, and in that situation they become fecundated. The female 

 [see figures] then takes to the water, and the skin of her back swells, 

 and forms cellules, in which the eggs are hatched, and where the 

 young pass their tadpole state, for they do not quit their domicile 

 till after the loss of their tail and the development of their legs. 

 At this period the mother leaves the water, and returns to dry 

 land. 



Swammerdam gives the number of eggs in a female frog as 1400, 

 and M. de Montbeillard counted 1300. In these eggs there is a 

 greenish albumen which is not easily coagulable. The yolk or vitellus 

 is absorbed by the embryo, and an abdominal cicatrix indicates the 

 umbilicus in young individuals. It is not rare to meet with double 

 germs in a single egg, but most of these prove abortive, though some 

 produce monsters with two heads, six legs, and two tails, as well as 

 hermaphrodites. In our climates, the early part of the spring is the 

 season of mating, when the frogs and toads of both sexes quit the 

 localities of their late hybernation and their ordinary haunts, and 

 move instinctively to those stagnant waters which are proper for their 

 purpose, and where they are then collected in swarms. 



The young of the Amphibia enter life under an entirely different 

 form from that which they are afterwards to assume ; and undergo, 

 like the insects, a series of metamorphoses or transformations, till 

 they arrive at their perfect state. In their first stage, the young have 

 an elongated body, a laterally compressed tail, and external branchiae ; 



