14 HAY. [Vol. IV. 



Amphibia, their development would be retarded until some fortu- 

 nate day when a heavy rain would make it possible for them to 

 reach permanent water. 



I now proceed to describe the structure of the larval Amphiuma 

 as disclosed by the contents of the eggs under consideration. 

 In my attempts to unravel this structure, I have depended 

 partly on dissections made by means of lens and needle, but 

 mostly on stained sections cut and mounted serially. 



I. The Skull. 



In Fig. 3 we have a view of the cartilaginous cranium seen 

 from above, and in Fig. 4 a view of the same from the side. 

 What will probably first strike the attention of the observer 

 is the existence, in the basilar region, of two fontanelles in the 

 cartilage, one on each side of the middle line. They are of an 

 elongated oval form, and are of such size that they leave only 

 a narrow strip of cartilage between them, and a similar ledge 

 along the inner and lower border of each otic capsule. Both 

 before and behind these fontanelles, the cartilage passes from 

 one side of the skull to the other. This portion of the primitive 

 skull is worthy of comparison with the adult skulls of Nectunis 

 and Siren. In Nectunis the trabeculas cranii are not connected 

 by cartilage behind the pituitary region, and have but a narrow 

 band connecting them in the exoccipital region ; so that there 

 is no cartilage in the floor of the brain-case behind the ethmoidal 

 region until immediately in front of the foramen magnum. In 

 Siren there exists, opposite the middle of the otic region, a 

 band of cartilage that passes from side to side. Behind this, 

 there is in the middle line a single fontanelle ; and this is limited 

 behind by the cartilage of the basioccipital region. The anterior 

 ends of the two fontanelles of Amphiuma come much further 

 forward than does the single one of Siren. 



In the narrow strip of cartilage between the two basal fonta- 

 nelles is seen the anterior end of the notochord extending well 

 forward toward the pituitary space. 



In the exoccipital region the condyles project prominently 

 backward, after the manner of those of the adult. The deep 

 notch between them is occupied by the tooth-like process of the 



