[9] OYSTER CULTIVATION IN THE NETHERLANDS. 1009 
solid type. The cells of the mesoderm, whose origin I cannot state with 
absolute certainty, but which appeared to me to be a product of the en- 
toderm, do not form a continuous sheet or leaf, but begin to be differen- 
tiated at a very early period into embryonic muscle and connective 
tissue. The preconchial invagination begins to make its appearance 
at a very early stage, the cells of the ectoderm being distinguished by 
their high cylinder-shaped appearance; the shell therefore belongs to 
very early embryonic formation; in young oysters the post-larval shel! 
of which has already formed, the embryonic shell can still be very dis- 
tinetly observed. [Full information as to the results of my observations. 
of oyster embryos, made principally on cross-section, are at the disposa, 
of the Commission, in case they should desire it for their final report. 
As regards the investigations relative to the young oyster, after it has 
settled, Dr. Hubrecht writes: “The time which I spent at the station in 
June was almost wholly devoted to the regulation of the physico-me- 
teorological observations, the prelimary results of which will be pub- 
lished in full at some future time. Onmy return in August, we made a 
distribution of the work assigned to us, and I was commissioned to oe- 
eupy myself with the oyster larve and their settling on the tiles, but 
was much delayed in my work by the long-continued unfavorable and 
. cold weather. Regular observations were out of the question during 
this month, the season of the settling of the oyster spat having been 
brought on prematurely by the hot weatherin July. I was therefore 
obliged to abandon the task which I had set myself for this year, and 
devoted all the time I could spare from the physico-meteorological ob- 
servations, to the study of the anatomy of the oyster, more especially 
of those points on which the opinions of scientists differ very much, and 
where there are still important gaps in our knowledge, viz, the heart 
with the pericardium, the organ of Bojanus, and the channels through 
which the generative products are emitted. I made numerous micro- 
scopic sections of one to three year old oysters; but these results of these 
observations I shall reserve for our final report, because it will require 
the uninterrupted observations of another summer, to bring this inves- 
tigation to a satisfactory close.” 
Dr. Van Rees writes regarding his observations on the radius of dis- 
tribution of the oyster spat and the conditions under which they settle, 
as follows: “ Whilst at the zoological station during the second half of 
June I noticed the forerunners of the oyster spat. To my great regret 
I was not able to be in Bergen op Zoom during July and continue my ob- 
servations at that place. When Ireturned during the last days of July, 
T noticed that a great deal of spat had settled. By fishing in different 
places I found, however, numerous oyster larvee swimming about in the 
rater, which could be kept alive for several days in sea-water contained 
in wide, open glass jars. In fishing I used the tow net in the manner in 
which Thad seen Professor Weismann use it in the Lake of Constance. 
The tinned iron hoop of the net is furnished with a long, free bag of very 
S: Mis: 2964 
—_ 
