Nidification and Eutbnjological Develojwient 29 



Several species were from different localities and these as well as each race 

 were kei)t in separate aciuaria. Observations were made several times each 

 day at intervals of three or four hours. Each jar was labeled and the egg 

 capsules lettered or numbered as they were deposited by the animals. 

 Notes were kept of developments in each capsule. The data which follow 

 have been condensed from the original notes. 



The information sought in these studies was to ascertain the time re- 

 quired for development and the rate of growth of the shells of the young 

 snails during their life in the aquaria. 



[a] Self-fertilization or Autofecundation 



That self-fertilization or autofecundation is possible among the fresh- 

 water pulmonates has been suggested by several zoologists during the past 

 hundred years or more, but until comparatively recent time few experi- 

 ments have been carried on to test the reality of this method of reproduc- 

 tion. Colton (1912. \). 173; 1918, p. 48) has shown that Lymnaea, Physa, 

 and several groups of Planorbidae {Gyraulus, Menetus) lay fertile eggs 

 by this method when isolated. Crabb (1927) has presented elaborate data 

 on this subject, and more recently Larambergue (1939) has issued an 

 elaborate monograph particularly relating to Bidimis contortus. On pages 

 541-543 he ]iresented a list which includes all of the authentic exami)les of 

 autofecundation. This list includes all families of Basommatophora as well 

 as a few among the Stylommatophora. Crabb (1927) studied Lymnaea 

 stagnalis appressa {=jugularis) to determine whether snails kept in strict 

 isolation reproduced by self-fertilization or b}' parthenogenesis. His con- 

 clusions were that there was no evidence of parthenogenesis in this snail. 



It is to be noted, however, that reproduction by parthenogenesis does 

 occur in some groups of snails. Boycott (1919) has asserted that Palude- 

 strina jenkinsi develops by this method. ]More recently Van Cleave ( 1937) 

 and ]\Iattox (1937, 1938) have shown that the viviparoid snail Campeloma 

 rufutn develops solely by parthenogenesis although other species of the 

 genus have been found to be bisexual. The reproductive method in Campe- 

 loma was observed by morphological and histological studies and there is 

 no question concerning the parthenogenetic method of reproduction in 

 the species examined. 



Some years ago, Chadwick ( 1903, p. 265) conducted some interesting 

 exi)eriments on Planorbis vorte.v, a common English planorbid. On Feb- 

 ruary 2, 1901, he isolated an adult specimen in a jar three-fourths filled 

 with boiled water, a small quantity of weed was introduced, the rest of 

 the jar was filled with pure oxygen and the vessel was perfectly sealed. 

 It remained in this condition for eighteen months, or until August, 1902. In 

 June, 1902, aften sixteen months of complete isolation, the snail deposited 

 some eggs which were hatched in early July, producing twenty-seven young 

 snails, many of which were still thriving under these confined conditions 

 on December 10, 1902. In evaluating this set of observations, and many 

 others along this line, it should be remarked that only those experiments 

 in which individual eggs were isolated have any conclusive value in estab- 

 lishing the occurrence of self-fertilization. This is especially true when 

 forms are considered for which there are no observations as to the length 

 of time the spermatozoa remain viable following copulation. 



