324 LOWER VERTEBRATES. 



" The eggs are quite remarkable, when compared with those of other Batrachians, for 

 their great size, the yelk alone measuring one fourth of an inch in diameter. In 

 almost every instance, on removing the operculum, the embryo, however small, was 

 found just beneath it, and thus occupying a position on the yelk which has the nearest 

 proximity to the air. 



"In the earlier stages . . . the head is broad and flat, the cerebral vesicles are easily 

 detected, the lateral portions not having united on the median line ; the eyes were 

 prominent and black ; the spinal canal was closed, and the ventral laminiB were just 

 beginning to extend upon the upper surface of the vitellus ; the arms consisted of 

 pyriform processes from anterior portion of the trunk, but the legs consisted of oval 

 masses entirely disconnected with the parts surrounding the vertebral column, and 

 seemed to have an independent centre of growth, and therefore did not bud out 

 from the trunk. In all of the earlier specimens these branchial appendages were visi- 

 ble on each side of the head. The general aspect of the embryo, as it lies extended 

 on the surface of the yelk, reminds us of the larval condition of salamanders and 

 tritons. In a later stage, as exhibited in another series of embryos, the external bran- 

 chiae had disappeared ; the legs, now united with the trunk, were terminated by an 

 expanded extremity, the rudiment of a foot ; the ventral laminae as represented by 

 the dotted line, extended farther down upon the yelk, but still this last was to a great 

 extent, uncovered ; the nostrils were visible, as round terminal depressions, but it was 

 not ascertained if they communicated with the mouth. A small branchial fissure was 

 detected on each side of the neck, and within this, as was shown by slitting open the 

 mouth and oesophagus, there existed on each side a series of fringed branchial arches. 



" The most extraordinary feature, however, of this stage was the peculiar change 

 going on in the yelk mass ; the whole of the yelk substance was moulded into a 

 spiral coil, and invested with a thin tunic, and thus converted at once into a spiral 

 intestinal canal, the coils of which extend from the sides of the trunk to the most 

 prominent portion of the yelk, and then, changing direction, and occupying the axis of 

 the coil, the intestine passes back again towards the trunk. The whole yelk-mass is 

 therefore moulded into a spiral intestine. In none of the instances which fell under 

 my notice had the final metamorphosis taken place. But Bonnet, Dumeril, and others 

 have observed that the tadpole remains in the dermal sac until its limbs are perfectly 

 formed and the tail has been absorbed ; until, in truth, it arrives at the same stage 

 reached by the common toad ; when, having finished its aquatic life, to which it is no 

 longer adapted, it leaves the water and seeks its livelihood in a more congenial man- 

 ner on the land. 



"In addition to the unusual circumstances under which these animals are developed, 

 it will be seen that they are objects of especial interest in connection with the general 

 subject of the development of Batrachian reptiles. The first peculiarity which may 

 be noticed is as to the period at which the arms and legs make their appearance. The 

 tadpoles of frogs and toads acquire a comparatively advanced stage of development 

 before any traces whatever of limbs are seen ; they leave the egg, increase in size, and 

 after a period (variable in the different species) of weeks or months, the rudimentary 

 arms and legs begin to be found. In Pijoa they appear before the external branchiae 

 disappear, and before even the ventral laminae descend upon the sides of the vitellus. 

 The development of the limbs independently of the vertebral column is an interesting 

 morphological fact. 



" That the first trace of a leg is an oval mass, entirely free and detached from the 



