THE DEVELOPMENT OF APLYSIA PUNCTATA. 499 



work very incomplete^ nnd it is therefore the inteutiuii of one 

 of us to attempt to continne it and follow the metamorphosis. 

 There would seem to be some liope of success if the metliods 

 of prepared sea-water and special feeding Avere nsed, such as 

 have beeu employed so satisfactorily at Plymouth in rearing 

 Echinoderms. 



The living embryos are very opaquCj and little can be seen 

 of their organisation. As was the case with the work done 

 previously on the cell-lineage, our observations were all made 

 from preserved material. The eggs are enclosed in gel.'itinoas 

 capsules^ and these are suspended in a long thread of jelly. 

 Carazzi made tlie following calculations : — there are on an 

 average seven eggs in each capsule in A. punctata and 

 fifty in A. limacina; the whole thi-ead, or '•'nest," as he 

 calls it, will therefore contain on an averao-e 80,000 esfirs in 

 the former species and 2,000,000 in the latter; this last 

 immber may at times be as high as 3,000,000. All the eggs 

 develop Avitli the exception of a few, which are not fei-tilised 

 or are abnormal from some other cause. In the later stao-es, 

 when movement is active and the muscles fully developed, the 

 embryos will contract very considerably on tlie addition of the 

 fixing agent, and this renders them difiicult to interpret. To 

 avoid this a 2 per cent, solution of cocaine in sea-water was 

 used, which narcotises them in a few minutes and makes it 

 easy to obtain preparations of fulK'-extended embryos. It is 

 troublesome, and takes much time to extract the embi-yos alive 

 fi'om their capsules, and the great majority get injured in the 

 pi-ocess. Most fixing agents do not harden the jelly, and it 

 is therefore equalh^ difficult to extract the embryos when 

 fixed by most of the common means. Formol, however, lias 

 the effect of hardening the j'r'Hy, and it is on this account 

 extremely useful. Alone it makes a good fixing agent, but 

 subsequent staining is rendered easier if it is used in combina- 

 tion with some other fixative. At the suggestion of Prof. Mever 

 a solution of formol and picric was used, made up in the 

 following Avay : — ten parts 40 per cent, formol, ten parts 1 per 

 cent, picric, eighty parts sea-water. This proved to be by 



