cat. These all belong to the species domestica, but are separated on 

 account of their color into different varieties. 



"The theory of evolution has led scientific men to recognize the 

 fact that species and varieties do not exist in nature, life being a con- 

 tinuous whole, the simple animals developing into complex animals, 

 and these again into still more complex forms of life, until the animals 

 and plants have reached the myriad varieties we see about us to-day. 

 Species are useful only, as I said before, as a means of identification, 

 enabling us to compare the animals, or fauna, of one locality with 

 another. But I am wandering from the question which you asked 

 me. A species may be described as a group of animals which have 

 certain characteristics not shared by any other living animals, while 

 a variety is a group of animals closely related to the species, and con- 

 nected with it by living gradations, but which have become slightly 

 different through occupying a different part of the country, or by living 

 on different kinds of food. A variety is sometimes called a geographic 

 race. Man is one of the best examples of the difference between 

 a species and a variety, and you are probably all familiar with the 

 different races of men." 



Howard, who had never studied scientific subjects before, asked 

 Professor Parker what the word Linne meant, after Limncea staynalis. 

 The Professor replied that this was the name of the great Swedish 

 naturalist, Carl von Linneeus, or Linne, as it is frequently written. 

 "The name of a person after the title of a species," he continued, 

 " indicates the investigator who was the first to give the animal that 

 Latin name, and by the presence of his name the student is able 

 to refer to the original description of the animal or shell." 



Professor Parker told us that it was always a good plan to make 

 a collection that would contain the largest possible variety, illustrat- 

 ing all of the principal divisions of the Mollusca. This would, he 

 said, be of great educational value to us, and would enable us to 

 better understand the almost infinite diversity of form in this class 

 of animals. 



Many collectors, he added, made a generic collection, which em- 

 braced several representatives of all the genera. The Professor then 

 impressed upon the quartette the importance and value of making a 

 complete collection of the mollusks which lived in their immediate 

 neighborhood. 



In the course of the conversation George asked into how many 

 classes the Mollusca are divided. The Professor replied by placing on 

 his blackboard what he called an artificial key, which read as follows: 



146 



