J_ 



_L 



_L 



_L 



Centimeters 



Figure 21. — Shells of C. gigas (left) and C. virginica (right) grown on soft, muddy bottom. Note the remarkable simi- 

 larity in the shape, size, and sculpture of the two species of oysters. The C. gigas was obtained from the northern 

 part of Puget Sound and the C. virginica from Georgia. The shells of the two species can be distinguished by the 

 absence of pigmentation of the muscle impression in C. gigas and by its lighter shell material. 



height — 20.6 cm. (8.1 inches); height of left and 

 right beak — 5.5 cm. (2.1 inches) and 4.5 cm. 

 (1.75 inches) respectively; length of shell — 9.7 

 cm. (3.8 inches); maximum width (near the 

 hinge) — 6.5 cm. (2.6 inches). The total weight 

 was 1,230 g., the shell weighing 1,175 g., the meat 

 35.8 g., and the balance of 19.2 g., representing 

 the weiglit of sea water retained between the 

 valves. Apparently the largest oyster recorded 

 in American literature is the giant specimen from 

 the Damariscotta River, Maine, reproduced in 

 natural size by Ingersoll (1881, pi. 30, p. 32). 

 Tliis shell is 35.5 cm. (14.3 inches) in lieiglit and 

 11 cm. (about 4.4 inches) in length. 



SHAPE OF SHELLS 



The shells of many gastropods and bivalves are 

 spiral structures in which the convolutions of the 

 successive whorls follow a definite pattern. Tiie 

 spiral plan is frequently accentuated by ridges, 



furrows, spines and nodides, or by pigmented 

 spots which repeat themselves with remarkable 

 regularity. A spiral structure is not restricted to 

 mollusk shells. As a matter of fact, it is very com- 

 mon throughout the animal and plant kingdom as 

 well as in architecture and art. Examples of a 

 great variety of spirally built organisms and 

 structures are given in the beautifully illustrated 

 books entitled "Spirals in nature and art" and 

 "Curves of life" (Cook 1903, 1914). As the title 

 of the second book implies. Cook is inclined to 

 attach some profound significance to the kind 

 of curves found in animal and plant forms. This 

 view, inherited from the philosophers of the 18th 

 and 19th centuries, considers the spiral organic 

 structures as a manifestation of life itself. The 

 influence of this philosophy persisted among some 

 scientists until the thirties of the present century. 

 It can be found, for instance, as late as 1930 in the 

 writings of a French physiologist, Latrigue (1930) 



MORPHOLOGY AND STRUCTURE OF SHELL 



21 



