SPAWN OF DORIS TUBERCULATA. 507 



sules are included two, three, or sometimes four em- 

 bryos, all moving about with the greatest activity, 

 and tumbling over each other apparently in high 

 glee and enjoyment. 



We will, however, select an example for special 

 description : 



The spawn of the Doris tuberculata is a broad gela- 

 tinous riband, attached by one of its edges to the 

 under side of stones in a circular coil of about three 

 volutions, the whole forming a beautiful cup- or 

 flower-like expansion. The number of ova imbedded 

 in it cannot be less than 50,000. Each egg contains 

 a single yelk ; but frequently there are two, and some- 

 times even three yelks in the same egg. The period 

 necessary for their attaining perfection is generally 

 about a fortnight, after which time the mass presents 

 a very animated spectacle. When examined with a 

 common magnifier, the full-formed embryo may be 

 seen in some, whirling itself round with great velocity 

 in the transparent egg ; others, having broken the 

 shell, will be found performing more extended gyra- 

 tions in the general envelope ; while others, again, are 

 swimming hither and thither in search of an aperture 

 through which to escape into the open water. 



The nascent animal forms a beautiful object for the 

 microscope. Its body is enclosed in a very delicate, 

 calcareous, nautiloid shell, furnished with an equally 

 diaphanous operculum; and the whole surface of the 

 little creature is covered over with minute vibratile 

 cilia, as are also the internal walls of the alimentary 

 canal, which is visible through the transparent cover- 

 ing. Two broad wing-like flaps form a very effi- 



