20 Bulletin Wisconsin Natural History Society. [Vol. 9, Nos. 1-2. 



(Plate I, Fig. 2) or tigrinum. This greater size is due not so 

 much to the number of eggs present — for this may be as great in 

 tigrinum as in punctatum — as to the greater thickness of the 

 common jelly mass. The photograph does not differentiate the 

 common gelatinous envelope of A. jeffersonianum, which is ex- 

 tremely thin. 



As a result of these differences in the thickness of the com- 

 mon gelatinous envelope we find decided differences in the con- 

 tour of the egg masses of the three species. In A. punctatum 

 the outlines of the individual egg envelopes are obliterated in the 

 general contour; in A. jeffersonianum they are almost perfectly 

 preserved, the entire cluster bearing some resemblance to a bunch 

 of grapes. In other words, the eggs of A. jeffersonianum form a 

 much looser cluster than those of A. punctatum. The egg masses 

 of A. tigrinum occupy in this respect an intermediate position. 



A further distinction between species is that the egg masses 

 of A. punctatum possess in general a greater degree of rigidity 

 and firmness, due perhaps to a denser consistency, perhaps to the 

 greater bulk, of the jelly. In this respect also, A. jeffersonianum 

 presents the opposite extreme, A. tig. :1111m occupies an inter- 

 mediate position. 



The eggs of A. punctatum and A. tigrinum are aggregated 

 more closely, forming a more compact group, than those of A. 

 jeffersonianum. 



The eggs of A. punctatum average slightly larger than those 

 of A. jeffersonianum. There seems to be greater variation in the 

 size of the latter. The range of the diameter of the two species 

 apparently overlaps. Accurate measurements are desirable as a 

 basis for the comparison. 



In the egg masses of A. jeffersonianum there is often observ- 

 able an arrangement of the eggs in from two to three spirally 

 arranged parallel rows. In punctatum I have found no such 

 tendency. 



The eggs of all three species are invariably attached to some 

 object — the stems of plants, leaves, twigs, etc. In the natural 

 environment the presence of air bubbless in the jelly mass is a 

 normal occurrence ; they are shown in the photograph of the egg 

 mass of A. jeffersonianum. 



