234 THE AM ERIC AX MUSEUM JOURNAL 



teeth measured six inches was approximately eighty feet, an estimate, 

 by the way, which was made many yeaivs ago by Professor Goode. The 

 largest Hving shark is the Whale Shark, Rhiuodon which probably does 

 not exceed fifty feet in length. 



In spite of its great size, Carcharodon appears to have been cjuite 

 common in its dav, judging at least from the number of teeth found in 

 the deposits of phosphate. And from this fact one may. form an idea 

 of the richness of the marine fish fauna of that time. For where there 

 existed one of these sharks there must have l>een a vast number of fishes 

 of the usual bony-fisli type, for sharks are proverbially rapacious, and 

 we can estimate "fairly that the daily provisioning of so huge a creature 

 implies the capturing of tons of bony-fishes. This is worthy of mention 

 also, because it gives us a striking illustration of the imperfection of the 

 geological record. It is a well-known fact that in regions where the 

 teeth of this shark are plentiful, there occur few fossils of the common 

 kinds of fishes. Even the most fragmentary remains of bony-fishes 

 (teleosts) are usually lacking. It is none the less clear from the very 

 presence of the sharks that a contemporary fish-fauna must have been 

 represented in the most abundant way. 



Bashford Dean. 



EXPERIMENTAL WORK WITH POMACE FLIES. 



EXPERIMENTAL studies in evolution are important not only for 

 their theoretical interest, but also because it is believed that the 

 principles worked out in the lowest forms of life will apply also 

 to domestic animals and plants and even to man. 



It is the natural course of scientific progress for verbal description 

 and speculation to be followed by mathematical statement and experi- 

 mental analysis. Certain experiments were made even before Darwin's 

 time and a large part of Darwin's own work was experimental; but 

 the painstaking studies of de Vries concerning the origin of plant species, 

 together with the recognition of Mendel's Laws of Heredity, not only 

 have given an impetus to experimental evolution, but also, in a large 

 measure, have determined the character of the work. As a consequence, 

 research by pedigree breeding for de Vriesian "mutations" and the 



