DEVELOPMENT OF BALANOGLOSSUS KOWALEVSKII. 115 
essentially the same as in B. minutus. In the anterior 
region of the notochord of B. Brooksii there are hardly any 
nuclei at all. I hope to publish figures illustrative of the later 
development and anatomy of the other parts at no distant date. 
APPENDIX. 
Methods.—From the characters of the unfertilized egg 
of B. Kowalevskii it was extremely improbable that the 
earliest stages of development could be passed anywhere else 
but in the mud which the parents inhabit. Though the exami- 
nation of Agassiz had failed in the attempt to find any but 
adult Balanoglossus in this situation it seemed worth repeating. 
Accordingly a large quantity of mud inhabited by Balanoglossus 
was placed in a glass vessel of water and worked up, avoiding 
rotatory currents, until the whole was in suspension. A number 
of Balanoglossus which had previously been minced very finely 
were then thrown in and the whole was then left to settle for a 
few minutes. I then siphoned off the water and lighter parti- 
cles in suspension, which consisted chiefly of vegetable débris, 
stopping the siphon when the layer of chopped Balanoglossus 
was reached, which could easily be seen by the bright orange 
colour of the fragments. This portion was drawn off and 
examined separately. It was found to contain great numbers 
of larve and embryos of Balanoglossus, minute Nemertines, 
free Nematodes, &c. In this manner all the animals 
living in several hundredweight of mud may, in an hour or 
two, be collected into about a pint of water and sorted with a 
simple microscope. This was generally performed by rotating 
a little of the water in a shallow saucer with a slight peripheral 
groove. The larve then all lie in the groove which may be passed 
under the lens by rotation. After a little practice it is of 
course unnecessary to discolour the water with fragments of 
the animal required, as of course the right layer can easily be 
detected by the size and character of the particles composing 
it. It appeared to be worth mentioning this mode of obtaining 
mud larvee as its application on a large scale does not seem to 
be generally employed. It should be remarked that small 
