IXVEhTEBRATES. WIXDOW GROUPS 45 



exposes the worm.s within the l)urro\vs. Several species of these are 



represented. 



In the Mollusk Alcove window is shown the natural history of a 



sand-spit at Cold Spring Harbor, Long Island, including some of the 



shore moUusks and their associates. The entrance of 



,,°^^ , the harbor is seen in the distance. In the foreground 



MoUusk , 1 ,■ 1 1 • 111- 11 1 



Qj.Qy at tlie edge ot the sand-spit a nuissel-l)ed is exposed by the 



receding tide over which fiddler-crabs are swarming into 

 their burrows. Beneath the water surface an oyster is being attacked 

 by a star-fish, while crabs and moUusks of various species are pursuing 

 their usual activities. 



The window group in the Vertebrate Alcove shows the piles of 



an old wharf at Vineyard Haven, Mass. Below the low- 

 ^ ^ ^ tide mark the submerged piles are covered with flower- 

 like colonies of invertebrate animals. Among these 

 are sea-anemones, tube-building worms, hydroids, mussels, seamats and 

 several kintls of ascidians or sea-squirts. The latter are primitive 

 members of the Chordate group which includes the vertebrates. Like the 

 embryo of man, they possess during their larval period a chorda or cartila- 

 ginous spine. At first they are free swimming but later in life many of their 

 organs degenerate antl they become fitted to a stationary mode of life. 

 Other exhibits illustrate certain facts made clear by Darwin, and 

 those who came after him. On the left facing the entrance variation 



under domestication is illustrated by dogs, pigeons, and 

 TT^H^ ^°^ domesticated fowls, the wild species from which they have 



Domestication ^^^^^ derived being shown in company with some of the 



more striking breeds derived from them. 

 On the right, various exhibits will show variation in nature. 



An example of this is the variation among the finches 

 yana ion ^^ ^j^^ genus Geospiza in the Galapagos Islands. 



Other examples show by means of a series of moUusks 



the range of color variation within a single species of West Indian 



Sun Shell, variation of sculpture within a single genus of land snail, 



and oscillation of variations about the normal type of the common scallop. 



The struggle for existence is portrayed by the meadow mouse, 



surrounded by its many enemies and yet continuing 



rugg e or ^^ maintain an existence by virtue of its great birth rate. 

 Existence ' 



The simpler features of the laws of Heredity as eluci- 

 dated by Mendel and his followers are illustrated by the inheritance 



,.^ of seed-coat color in the common pea, the color of sweet 



Heredity , . . ,. 



peas, and the coat-color of rats as shown m a series of 



panels in the neighboring case. 



[Return to the elevators.] 



