THE FROG. 



379 



the second they began to be agitated more 

 than before ; the males made a noise some- 

 what resembling the grunting of a hog; the 

 females only kept sinking and rising in the 

 water. 



The embryo is found, in the first place, to consist of 

 a small globular body, one side, or hemisphere, of which 

 is of a dark brown colour, the other being much paler. 

 In a very short period after the egg is deposited, four 

 hours, according to Rusconi, a deep furrow across the 

 dark hemisphere divides it into two equal parts, and this 

 is soon afterwards crossed by another at right angles ; a 

 third and a fourth furrow are produced, and so on, until 

 the whole surface of this side of the sphere is, as it were, 

 granulated. This appearance, however, is but transi- 

 tory, the surface soon becoming almost smooth. In the 

 course of the second day, the sphere begins to elongate, 

 and a groove, which had previously divided the upper 

 part of it into two equal parts, begins to close up. The 

 head becomes prominent, the tail begins to show itself, 

 the little hooks by which it subsequently lays hold of ob- 

 jects and supports itself, begin to appear. At this pe- 

 riod the examination becomes more easy, and more in- 

 teresting. At somewhat more than fifty hours in an ele- 

 vated temperature, the head is very well marked, the 

 tail somewhat elongated, and even the rudiment of the 

 membrane, or web, which is destined to form its fin, is 

 visible. About this time, also, a small projection takes 

 place on each side of the head, which is the earliest in- 

 dication of the branchiae, and the muscles of the spine 

 may just be seen. In figure 2 of the woodcut, I have 

 given an outline of the embryo in this condition. At 

 this time the water is seen to flow in a distinct and ra- 

 pid current to the branchial orifice over the rudiments of 

 the branchiae, which are now just visible, the course of 

 which current I have indicated by arrows. These parts 

 gradually become more developed ; the body is more 

 elongated, the branchiae more distinct; the fin extends 

 round the tail and partly over the back ; and the head is 

 distinguished from the body by a slight contraction at 

 the neck ; and a, short period more suffices to bring it to 



The male of the first couple ejected the hu- 

 midity with which his body was swollen, by 

 which the water in the glass was made mud. 

 dy ; and he soon after quitted the female. 

 Our philosopher continued for twelve hours to 



the condition represented in figures 3, 4, of the woodcut, 

 in which the branchiae are seen to consist of two tuber- 

 cles on each side, as yet simple and undivided ; the hold- 

 ers, which are small simple organs placed near the situ- 

 ation of the future mouth, and which serve to enable the 

 little animal to attach itself by means of a viscid secre- 

 tion at their extremities, have become longer, the web, 

 or fin, is also enlarged. By this time the first voluntary 

 motion of the embryo is discovered on the application of 

 any means of excitement or disturbance ; but it consists 

 only of a slight movement of the head or tail. The nos- 

 trils are seen more distinctly, but the mouth is scarcely 

 yet observable, and shortly afterwards the eye, in a ru- 

 dimentary state, may be just discerned. The next step 

 in the development is a slight division of the branchigs 

 into lobes, and the appearance of that beautiful and in- 

 teresting phenomenon, the circulation of the blood 

 through these organs. The embryo, which is still con- 

 fined to a curved position by the envelopes (fig. 1), is 

 now seen frequently to extend itself by sudden jerks, as 

 if to emancipate itself from its confinement, which it 

 eventually does by tearing the membrane of the egg. 

 The Tadpoles, we see, are now hatched (fig. 5). Ac- 

 cording to Rusconi, this takes place within four days 

 after the deposit of the eggs, in a temperature varying 

 only from 23 to 27 Ceutigr. (73. 4 to 80.6 Fahr.); 

 but certainly in our own climate, in the ordinary tem- 

 perature of our spring, it does not take place until at 

 least a month. As I before observed, the development 

 may be greatly hastened by a constant elevation of tem- 

 perature, and I was often surprised at the degree to 

 which this was the case in the course of my own obser- 

 vations ; but the comparatively low temperature of our 

 spring, and the cold frosty nights which occur in March 

 and April, may well account for such a discrepancy. 

 If the eggs be deposited at the middle or latter end of 

 March, it is generally, with us, the latter end of April 

 before they are hatched. The situation of the mouth is 

 now distinctly visible, though the opening is but small; 

 and even when it becomes considerably enlarged it has 

 no power of movement, and there are no distinct' lips. 

 The branchiae now speedily enlarge, and each of the two 

 branches on either side is seen to consist of about four 

 leaves (figs. 6. 9); these are sessile upon the body or 

 stem of the branchia; they are somewhat granular on 

 the surface, and slightly irregular in their form; there is 

 also frequently a short additional branch at the base of 

 the posterior one, as is shown in the outline, figure 9. 

 The present state of these organs, which have now ar- 

 rived at their maximum of development, constitutes one 

 of the most charming objects for microscopic observation 

 which can be conceived, and to view which a very high 

 power is not necessary, nor even desirable. The current 

 of the blood poured in regular pulsations at each ccn- 

 traction of the heart, passes up each stem or main branch 

 of the branchiae, and a distinct stream is given off to 

 each leaf; it is propelled to the extremity, and then re- 

 turns down the opposite sides in the most regular man- 

 ner, and the parts are so transparent that every globule 

 of blood is distinctly and beautifully visible. 



This state of things, however, is- destined to last but 

 a short time. No sooner have these interesting organs 

 attained their greatest development than they begin to 

 diminish in size ; they become obtuse (fig. 7,) and are 

 gradually so reduced as to be withdrawn within the bran- 

 chial cavity, and concealed by a little operculum of the 

 intepument. The eyes are now perfectly formed. The 

 holders have become much diminished in size; thu 



