326 EDWARD D. AND RUBY M. CRABB. 



PLATE I. 



Figs. i6 and 10-13 are of Lymncea stagnalis appressa eggs; Figs. 7-9 are of 

 L. palustris eggs. All figures except Fig. 2 were drawn with the aid of the camera 

 lucida to the scale shown in the plate. The eggs represented by Figs. 3 and 12 

 were mounted in a very weak solution of formaldehyde in a slide having the pits 

 so shallow that the covers flattened them somewhat. 



Explanation of Figures of Polymtelline Eggs. 



1. An egg having four vitelli. The dotted line represents the extent of a mass 

 of sperms in the albumen. 



2. Five unreduced vitelli occurring in a single section through an egg. The 

 first maturation spindle is shown in one ovum, and an aster of a first maturation 

 spindle is shown in another. 



3. An egg laid by a wild snail, showing seven vitelli. Yolk globules have been 

 extruded from four of the vitelli. 



4. An egg having seven vitelli in sixteen to thirty-two-cell stages. 



5. An egg with three vitelli in early cleavage stages. The dotted line indicates 

 the extent of a mass of sperms in the albumen. 



6. An egg having seven vitelli which have not given off the first polar bodies. 



7. Lymncea palustris egg with two advanced embryos, one of which probably 

 belongs in the small attached egg. 



8. An egg having two vitelli, one of which is in the four-cell stage. 



9. An egg having five vitelli in early cleavage stages. 



10. L. s. appressa egg having five vitelli in early cleavage stages. 



11. An egg having eight vitelli; one of which has disintegrated, while five are 

 undergoing normal cleavage, and the other two apparently have not divided. 



12. An egg having forty-six vitelli, laid by a wild snail. 



13. An egg having twelve vitelli in four to eight-cell stages. 



