32 
This ganoid is a surviving representative of a race of pale- 
ozoic fishes, from which all living fishes (except the sharks 
and lung fishes) are descended. There are reasons on 
the side of paleontology for believing that this ganoidean 
group is derived from the line of the ancient sharks ; it is 
now of especial interest that the study of the earlier stages 
of the gar-pike which this valuable, and in fact unique 
material represents, tends to confirm this view. The eggs 
were fertilized artificially. 
147. ADULT GAR-PIKE. 
148. Zeigler models illustrating the EARLY DEVELOPMENT OF 
SHARKS, illustrated by three models. 
By Dr. William Stratford (College of the City of New York). 
149. EGG-CASE OF THE PORT JACKSON SHARK, Cestracion galea- 
tus. From Southern Australia. 
150. YOUNG OF THE DUCK-BILL, Oruithorhynchus platypus. 
From Queensland. 
By Henry E. Crampton (Biological Department, Columbia 
College). 
I51. EMBRYONIC DEVELOPMENT OF SNAILS (Physa and Limnea), 
showing that the right or left spiral coils of the shell are pre- 
determined by the first stages of cell division of the embryo. 
The adult shell of Pxysa is spirally wound to the ft. The 
adult shell of Lzmnea, on the other hand, is spirally wound 
to the right. It is interesting to observe that these pecul- 
iarities of the adult shells are foreshadowed in the earliest 
cleavage stages of the embryo. In P#ysa, for example, 
the first group of micromeres are budded off to the /ft; 
in Limnea, to the right. 
152. EIGHT-CELL STAGE OF PHySA, showing the budding off to 
the /eft of the first group of micromeres. 
153. EIGHT-CELL STAGE OF LIMNA, showing the budding off 
of the first group of micromeres to the right. 
