493 A. U. CARR SACNDERS AND MAKfiARET POOLE. 



A numbei' of stages of A. limacina Avere also examined, 

 but the difference is insignificant. 



Carazzi states that Aplysia punctata disajjpears in May 

 to reappear again in the winter. We were able, liowever, to 

 obtain this species in large numbers until the middle of June. 

 No difficulty was experienced in keeping Aplysia in the 

 aquarium, and they laid eggs in great quantities. The eggs 

 develop normally, and equally well if kept in jars or in the 

 tanks with circulation, provided onl}^ that the water ])e 

 changed every two days or so. Early in the summer the eggs 

 were at times attacked by bacteria, Init if enough spawn was 

 kept it was alwa3's possible to have some at the stage required 

 in a healthy condition. Later in the year the eggs were 

 attacked by alg{e, and the embryos destroyed long before the 

 free-swimming stage was reached. This was a more serious 

 trouble than the bacteria, but the difficulty can be avoided by 

 keeping the spawn in filtered water in the dark, where the 

 algfe do not develop. The rate of development varies with the 

 temperature of the water. This is described by Carazzi for the 

 different species. In April some fiifteen days elapsed between 

 the deposition of the eggs of A. punctata and the emergence 

 of the free-swimming larvte from the capsules. It is possible 

 to keep the larv;e in jars for some time, but even though they 

 be kept in circulating water, they always die within a short 

 time without exhibitino- anv chano-e of structure. Mazzarelli 

 states that he kept some larvie of Bulla striata alive for 

 twentv davs, which is far longer than we ever succeeded in 

 keepingAplysialarva3, but even these showed no change during 

 that period. No one has yet raised any Opisthobranch larva? 

 through the metamorphosis, and there is therefore a large gap 

 in our knoAvledge of the embryology of the group, for not only 

 in the fiee-swimminy larva are certain adult oroans, such as 

 the heart and pericardium and the yonads and o-enital ducts, 

 entirely undeveloped, but the interpretation of some organs 

 in the larva, also must remnin doubtful until the further 

 development is known. Our failure to rear the larvae of 

 7\plysia beyond the free-swimming stage renders the present 



