AMBLYSTOMA PUNGTATUM. 9 



from the borly by the continued growth of the neck region ; the 

 branchial and brachial lobes are growing more prominent, and on 

 the median ventral line of the neck between the branchial lobes, 

 or slightly posterior to them, is a single rounded prominence which 

 indicates the pericardial region. The posterior end of the body, 

 owing to the development of the tail, which is stretching away 

 from the body, has become more elongated, and is obtusely 

 pointed. 



In a ventral view at this stage, the nasal pits are distinctly seen, 

 as two small, black cavities lying just within or ventral to, the 

 swellings of the optic vesicles. The head is seen to have become 

 much narrower and longer, and tiie position of the future mouth 

 is indicated by the space existing between the anterior end of the 

 branchial lobes and the curved outline of the extremity of tiie 

 neural canal. The beginning of the tail also shows distinctly, 

 and its median ridge, at the end of which is the dark cavity of 

 the anus, is now much increased in size. Plate 2, Figure 14. At 

 a period about two days later than that represented by Figure 14, 

 a new lobe or prominence is seen upon each side of tiie neck 

 between the eye and the branchial lobe; it is much smaller than, 

 and lies just at the anterior extremity of, the long axis of the 

 branchial lobe. Very often it is developed consentaneously with 

 the branchial lobes, instead of making its appearance a day or 

 two later. From these lobes are to be developed structures which, 

 from their resemblance to the balancers of Dipterous insects, have 

 come to be known as the "balancers." The eyes have progressed 

 rapidly during the last day or two, and the nasal pits are more 

 clearly defined. The body of the embryo is now, by a rapid 

 growth of the ventral side, losing the curved outline which it has 

 always had, owing partly to its having been formed upon a sphere, 

 and is now becoming straight; the caudal portion is developing rap- 

 idly and vertebrie will soon be seen making their appearance 

 within its substance. 



The animal now begins to show active, muscular movements, 

 which consist of a sudden doubling upon itself; a position retained 

 for a few seconds only, when it regains its original position by 

 an(jther sudden and violent movement of the body. A thickened 

 ridge also appears on either side of the anus; these are the walls 

 of the cloaca. Within a day or two, the ra|)idity of development 

 varying widely in different specimens, the branchial lobes show 

 3 



