2 Desor on the Embryology of Nemertes. 
others are slender, like a thread ; but the greater number are 
small and similar in shape to the common earth-worm. 
Among the species of this type found on the shores of New 
England, there is one very similar to the Nemertes olivacea 
of Johnston. It is one and a half to two inches long, and has 
the same dark green color, but without the red head, where- 
fore I shall designate it under the name of Nemertes obscura. 
(Fig. 1.) It lives under stones and among sea grasses on 
the shore, between low and high water mark. Several sve- 
cimens of this species were procured in East Boston, towards 
the end of January 1848; they were kept in a jar, where 
they lived several months in a very healthy state, care be- 
ing taken to renew the water every day. On the 12th of 
February, there was observed at the bottom of the jar a yel- 
lowish gelatinous string, (fig. 2), which was found to consist 
of eggs.. It had been laid during the night, and was re- 
markable as being almost as large as the parent animal. On 
examining it with a magnifying glass, (fig. 2a), I was struck 
with the irregular distribution of the yolk-spheres. Instead of 
being isolated and surrounded each by an independent 
albumen-like liquid, I found several of them collected together 
in transparent gelatinous bags, which seemed to be attached 
to a central string by a kind of neck or stalk, like a bunch of 
onions. ‘The bags themselves are generally spherical, with 
the exception of the terminal ones, which are elongated and 
truncated at their base. The stalk by which they are attached 
is hollow, and the whole body bears a striking resemblance 
to a Florence oil flask, (fig. 3,) whence in future I shall call 
them flasks. : | 
The number of yolks enclosed in a flask is generally three 
or four, seldom more than six or less than three. I have seen 
nevertheless, some containing ten and even as many as eleven, 
and.on the other hand, some with no more than one, in which 
! The same peculiarity is found in several species of Eolis, where there are com- 
monly three or four yolks in one egg : 
