32 The Nidus of Lunatia-heros. 



Nidus of Lunatia-heros. 



The Nidus, when found damp on the beach, presents the appear- 

 ance of a white rubber washer or diaphragm; somewhat resem- 

 bling an inverted shallow bowl, open at the top and bottom and, 

 considering its real make-up, is fairly tough and flexible. Sizes 

 vary from two to six inches in largest diameter, but the shape is 

 curiously constant. When dried they still preserve their shape, but 

 are naturally quite brittle. According to general appearance they 

 are constructed entirely of sand held together by some glutinous 

 substance; but on holding a specimen against the light we find it 

 is closely stippled throughout with transparent points. The thick- 

 ness of the nest is between -^ and yV of ^.n inch, and on separat- 

 ing the inner from the outer surface we at once see the honey- 

 combed character of the interior. 



Diagram of Transverse Section of Nidus. 



These interior cells are arranged in quincunx order, according 

 to Dr. Gould ; and with a small lens and a strong transmitted 

 light this statement is readily verified. There is but one layer of 

 cells in the thickness of the Nidus. The interior of the cell ap- 

 proximates spherical in form, and each cell is perhaps a trifle less 

 than ^V inch in diameter. Dr. Gould in his report states: "Each 

 of these cells contains a gelatinous t^g having a yellow nucleus 

 which is the embryo shell. " This hardly seems in accord with 

 the result of personal observation. Taking a transverse section of 

 the Nidus and examining the same with a power of 50 diameters, 

 one gets the decided impression that the greater portion of the 

 nest is made up not of sand but of the embryonic shells. The 

 surface and main portion of the walls between the cells consist of 

 layers of single grains of sand. 



