32O EDWARD D. AND RUBY M. CRABB. 



(often of the same mass) as there is between normal and poly- 

 vitelline eggs. This is also true of the vitelli. Abnormal vitelli 

 having the yolk protruding or flowing out, such as are shown in 

 Figs. 3 and 11, and even cases of absence of vitelli, are occasion- 

 ally found in eggs which to all other appearances are normal. 



Several eggs have been found adhering together, but in most 

 cases each one contained a single vitellus. In one instance (Fig. 

 7) two embryos are in a single egg while the other egg has none. 

 In another case three eggs are joined together; the two end ones 

 having no vitelli and the middle one having only two vitelli. The 

 most remarkable instance of adhering eggs is one in which six 

 normal eggs are joined in a string. However, there is nothing to 

 indicate that polyvitelliny is dependent upon such adhesion of 

 eggs- 



The maturation and early cleavage stages are apparently normal 

 in polyvitelline eggs having less than a dozen vitelli. In some 

 eggs having a larger number many of the embryos pass the 

 trochophore stage and some even reach the early shell stage be- 

 fore dying. The first maturation spindle is formed in a clear 

 area or " well " in eggs which have been laid and moves to the 

 periphery (Fig. 2) of the vitellus. The first polocyte migrates 

 out into the albumen and the second remains attached, as has been 

 shown is the case in normal eggs (Crabb, '2/0). 



We have never been able to hatch more than four snails from 

 a single egg, but we have succeeded in repeating this experiment 

 four times, and a fifth egg containing four embryos was killed 

 and mounted. By tabulating the data available on the viability 

 of polyvitelline eggs of L. s. apprcssa we find that of 53 eggs 

 having two vitelli each, 39 hatched each vitellus, 8 hatched only 

 one and 6 failed to hatch either vitellus. Of 5 eggs having three 

 vitelli, 3 hatched all three, and 2 hatched only two of the vitelli. 

 From 4 eggs containing four vitelli each, sixteen young were 

 hatched. Of 116 L. s. apprcssa hatched from polyvitelline eggs 

 not one was sinistral. 



OCCURRENCE OF POLYVITELLINY. 



Twenty-one Pliysa sa\ii, fifteen of which were hatched from 

 the same mass of eggs, deposited 348 masses containing 9,061 

 eggs, two of which had two vitelli each. 



