2G0 SEA-SIDE STUDIES. 



in a perfectly traiisi^arent membrane. The first thing 

 which will surprise you, on commencing the investiga- 

 tion, is that the division of the yolk-mass is unlike that 

 of most other eggs. In the first 2:)lace, it is not s^^m- 

 metrical ; in the next place, it is not always the same. 

 Sometimes the division occurs in two unequal halves ;* 

 sometimes in three, or even four, unequal parts.-f I 

 have even counted five. The germ-mass may develo]^ 

 into one, two, three, or even six embryos, \ all of which 

 are seen slowly rotating in the same envelope ; and 

 besides these, there may generally be seen various 

 masses of granules rotating with them, or driven about 

 within the envelope — which are probably fragments of 

 the germ-grass insuificient to form a separate embryo. 

 This multiplication of individuals from one egg, this 

 production of twins, or tii'plings, is a constant fact, and 

 may help the general question of twin births. Very 

 curious it is to watch the increasing activity of the 

 little embryos. At first their rotation is scarcely per- 

 ceptible ; after a while the long cilia protruding from 



* In the ova of an Actceon, which spawned in my vase, I observed 

 the same want of symmetry ; the yolk-mass divided in each case into 

 two unequal halves. 



f Conip. VoGT : Annales des Sciences, 1846. I. 24. 



X I hesitated to record in the text what I found in my Teiiby note- 

 book ; namely, that these embryos sometimes amount to as many as 

 six in one chorion, because as the observation was made when I was 

 comparatively new to the subject, and differed from what is said by 

 others, I thought it possible some error of interpretation might have 

 occurred. I have since satisfied myself that my original note was ac- 

 curate, and I have at this moment a coil of Aplysia eggs in process of 

 development, in some of which there are six, seven, and even eight em- 

 bryos actively rotating in each chorion. 



