76 



PROCEEDINGS OF THE AMERICAN ACADEMY 



Fig. 4. 



2d. Bv thickening the walls of the cell in proportion to its tendency 

 to become broader, and thus keeping the diameter of its cavity uniform. 

 3d. When the divergence reaches a certain amount, by making a 

 false-cell, with a pointed bottom, between the diverging cells. 

 On the concave side, -7— 



1st. By narrowing the cell towards its mouth. 



2d. "When two adjoining cells converge so much as to render the 

 mouth too small, the walls between them are suppressed at a certain 

 point, and thus the two mouths are merged, and the compound cell 

 thus formed has a double base, and but one entrance, the two cells 

 being combined, as are certain kinds of twin crystals, or of double 

 monsters. The form of the mouth under these circumstances is, how- 

 ever, liable to a considerable range of variation, as in the central line 



of cells in Fig. 4,* in which are a 

 variety of hexagons. That on the 

 line a, b has three sides at one 

 end, united by two long sides with 

 one at the other, and thus two of 

 ■/ the opposite sides are not parallel ; 

 at c, d, two sides at either end are 

 united by two long sides, these last 

 being parallel ; and at e, f, the 

 mouth of the compound cell has 

 seven sides. Each has a partition 

 at its base, separating the two orig- 

 inally distinct cells, and each was 

 lined with a cocoon, showing that 

 it had been used for rearing young. 

 In combining the mouths of two 

 adjoining cells, it will be seen that 

 this does not consist merely in 

 g suppressing the partition between 



them; for if this were so, each of the long sides would contain more or less 

 of an angle, as at the lower side of g, according to the degree of conver- 

 gence, until three of the sides of each of the combining cells had disap- 

 peared. Instead of this, the portions of two sides forming the angle just 

 referred to are replaced by one straight side, as on the upper side of g, 

 and in both of the long sides of the undulating line of cells above it. 



* Figs. 4, 5, and 6 are made from impressions obtained directly from the comb 

 and transferred to wood. Tiiey represent the forms of the cells exactly. 



... d 



