INVERTEBRATES. WINDOW GROUPS 35 



is seen in the distance. In the foreground at the edge of the sand- 

 Shore spit a mussel-bed is exposed by the receding tide over which 

 Mollusk fiddler-crabs are swarming into their burrows. Beneath 

 Group {] ie wa ter surface an oyster is being attacked by a starfish, 

 while crabs and mollusks 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 

 Wharf Pile submerged piles are covered with flower-like colonies of 

 Group invertebrate animals. Among these are sea-anemones, 



tube-building worms, hydroids, mussels, sea-mats and several kinds 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 carti- 

 laginous spine. At first they are free-swimming but later in life many 

 of their organs degenerate and they become fitted to a stationary mode 

 of life. 



In the northeast corner gf the Hall, a window group shows the animals 

 and plants of a rock tide-pool, the "Agassiz Cave," at Nahant, Mass. 

 Rock Under a natural bridge below a 60-foot cliff the falling 



Tide-Pool tide leaves a pool in a rocky basin, sheltered within 

 Group which is a community of sea-anemones, sea-stars, corals, 



sponges, hydroids and other animals living in the midst of a gorgeous 

 sea-garden of marine plants such as are common on the northern New 

 England coast. Through the arch of the natural bridge may be seen 

 a curious rock formation known as '"Pulpit Rock." 



Other exhibits illustrate certain facts made clear by Darwin and 

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

 Variation under domestication is illustrated by dogs, pigeons, and 



Under domesticated fowls, the wild species from which they have 



Domestication } )Qcn c i er i vec l 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 

 Variation example of this is the variation among the finches of 

 In Nature the genus (icospiza in the Galapagos Islands. 



Other examples show by means of a series of mollusks 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 variations 

 about the normal type of the common scallop. 



The struggle for existence is portrayed by the meadow mouse, sur- 

 Struggle for rounded by its many enemies and yet continuing to main- 

 Existence tain an existence by virtue of its great birth-rate. 



