20 THE NAUTILUS. 



fresh- water pulmonates) , either alone or in groups of one, 

 two, or more, but never exceeding six in any one group (as 

 far as observed). As a rule, many eggs were crowded in a 

 small space on the plant surface (see figures 1-3). On some 

 plants but one side of a leaf contained eggs while other leaves 

 contained eggs on both sides of the leaf. Several areas of the 

 leaves of different plants were measured and the number of 

 eggs in this area were counted, with the result shown in table 

 No. 1. These figures indicate the great abundance of the eggs 

 of this mollusk. The leaf used for attachment was generally of 

 a living plant, but in many cases the dead and partly decayed 

 leaves and pieces of plants were utilized for this purpose. 

 In the table all leaves were about 6 mm. wide. 



TABLE No. 1. Number of Eggs of Gillia altilis on Plants. 

 Plant. Length of Leaf. No. of Eggs. 



Vallisneria spiralis 50 mm. 70 



60 mm. 160 



50 mm. 22 



100 mm. 69 



75 mm. 132 



75 mm. 73 



90 mm. 68 



45 mm. 33 



The eggs are somewhat hemispherical in form, 1.25 mm. in 

 diameter, the thickness being about a third of the diameter. 

 Upwards of 80 per cent of the eggs contained living embryos, 

 the balance being dead; a number of these were filled with 

 protozoa. The envelope of the egg is very transparent and 

 the embryo is transparent enough to permit some of the 

 organs of the body to be seen through the mantle and trans- 

 parent shell. The heart, placed near the aperture of the shell, 

 was observed to pulsate very rapidly in all the embryos, in 

 one individual 87 pulsations per minute. 



Nearly all of the embryos were in an advanced stage of de- 

 velopment, the embryonic shell as well as the external organs 

 of the body rostrum, tentacles, eyes, operculum, etc. being 

 fully formed (fig. 4). The embryos moved about in the egg 



