THE FERTILIZATION PROCESS IX THE SXAIL. 91 



(a) ten chromosomes is the usual number found in young first 

 polocytes, and an equal number normally remains in the egg; (b) 

 the anaphase of the second maturation division usually shows ten 

 chromosomes at each pole and (c) the observed maximum number 

 of karyomeres which go to form the definitive egg pronucleus i 

 ten. 



X. CONCLUSIONS. 



From the evidence brought out in this paper it appears that 

 self-fertilization is the normal method of reproduction in L. s. 

 apprcssa and that in this snail cross-fertilization seldom or never 

 occurs. The reasons for concluding that self-fertilization is the 

 normal method of reproduction are as follows : 



1. Both ova and spermatozoa are developed in a single acinus 

 at the same time, and since the ovum soon loses its investing 

 membrane polyspermy usually occurs before it leaves the acinus. 



2. At no time are functional sperms absent from the hermaphro- 

 dite gland and duct in normal healthy adults, thus by the laws 

 of chance making competition of foreign sperms unsuccessful. 



3-^Free ova lacking a vitelline membrane are usually surrounded 

 by ripe sperms, numbers of which enter each ovum as it passes 

 through the acinus and hermaphrodite duct. 



4. There is no evidence of desquamation of the lining in any 

 part of the reproductive system, as has been described in Helix, 

 or of any other natural process which would cause temporary or 

 permanent, unisexuality in L. s. apprcssa. 



5. Individuals raised from isolated eggs and reared in strict 

 isolation reproduce as abundantly as do those in mass cultures. 



6. There is no evidence of gynogenesis or any other form of 

 parthenogenesis. 



7. Two polar bodies are extruded in eggs of virgins, the first 

 normally loses connection with the vitellus and by the time of the 

 first cleavage has migrated 50-200 micra into the albumen; the 

 second polocyte remains attached to the vitellus, but its chromatin 

 does not return to the egg nucleus. 



8. Ten chromosomes comprise the haploid number as is shown 

 by the first and second maturation divisions and by the number 

 of karyomeres in the mature egg. 



