520 Phylum Mollusca 



several times by decanting the water and refilling the dishes during the 

 next 24 hours to insure proper aeration and elimination of body fluids. 



The eggs of Chaetopleura are enclosed within a bristly chorion from 

 which they hatch as swimming trochophores in from 25 to 30 hours. The 

 larva is well supplied with yolk and therefore requires no feeding for 

 several days. In order to carry larvae through to metamorphosis it is 

 necessary to transfer them daily to dishes of fresh seawater by means of 

 a pipette. Otherwise they soon become infected with bacteria and tend 

 to develop abnormally. After the second day of larval life the shell 

 and foot begin to appear on the trochophore and these continue to de- 

 velop during succeeding days. In from 7 to 12 days the larva meta- 

 morphoses into the adult form and becomes a dorsoventrally flattened 

 creeping animal. It is possible to carry them through metamorphosis 

 without feeding but it is thought that transformation is hastened if the 

 feeding of diatoms is begun on the sixth day of larval life. This species 

 is used regularly in the embryology course at Woods Hole and no great 

 difficulty has been experienced in securing the complete development 

 of the larva including metamorphosis under laboratory conditions. The 

 young metamorphosed chitons may also be kept indefinitely by allow- 

 ing seawater to flow through the dishes in which they are kept a part 

 of each day. This supplies necessary food and ensures rapid growth. 

 Washing them free of sediment periodically is the chief requirement for 

 keeping the young animals in a thriving condition after metamorphosis. 



Bibliography 



Grave, B. H. 1932. Embryology and life history of Chaetopleura apiculata. J. 



Morph. 54:153. 

 Heath, H. 1899. The development of Ischnochiton. Zool. Jhrb. 12:567. 

 Kowalevski, A. 1883. Embryogenic du Chiton polii. Ann. Mhs. Hist. Nat. 



Marseilles. 5. 



Class Gastropoda, Order pulmonata 



LYMNAEA [=PSEUDOSUCCINEA] COLUMELLA* 



THE hermaphroditic snail Lymnaea [=Pseudosuccinea] columella, 

 when isolated, lays fertile eggs which are self- fertilized (Colton, 

 1912, 1918). This observation has been confirmed by Crabb (1927). 

 We can, therefore, establish a pure line in animals in the same way that 

 it can be done in many plants. 



A line was started in 191 1 and since then the descendants of the 

 original parent have been under controlled conditions for over 93 genera- 



* Abstracted at the suggestion of the authors from an article in Amer. Nat. 68:129, 

 1934. by Harold S. Colton and Miriam Pennypacker, University oj Pennsylvania. 



