256 A, A. W. HUBRECHT, 
terminates in the central fibrous bundle, continues its way 
directly through the tissue of nerve-cells, passes upwards in 
the space left free between the superior and inferior lobes 
(Meckelia somatotomus), finally to find its way into the 
cephalic furrows. The same sections with identical results 
were made by me of Borlasia olivacea from the Dutch coast ; 
nerve-cells and canal were quite as distinct. 
The cephalic sacs in the Borlasians must on these grounds 
be regarded as belonging morphologically to the ganglionic 
texture with which they are in uninterrupted continuity.! 
Now, as it is chiefly in this group that the ganglionic tissue 
contains a considerable quantity of hemoglobin, with its well- 
known property of binding free oxygen, and as the oxygenated 
sea-water has a free access to the hemoglobinous nerve- 
cells by means of the cephalic furrows and ciliated canals, I 
do not hesitate to regard the cephalic sacs as a special respt- 
ratory apparatus providing the cephalic hemoglobin with 
fresh supplies of oxygen. 
How this respiratory process in the central nervous system 
may inflnence the organisation and the life of these ani- 
mals remains for the present unexplained, as long as similar 
observations in other groups have not yet been made upon 
which comparative researches might be based. 
Generative Organs and Development. 
I have little to add to what is mentioned by Mr. MacIn- 
tosh under this head. The change which takes place in 
the interceecal dissepiments when the generative products 
make their first appearance, and the space occupied by these 
between the constituent plates of these dissepiments has been 
already mentioned above (Plate XIII, fig. 8). Genital aper- 
tures giving access to these cavities were present on the dorsal 
side of theanimal. Generally the emission of the eggs or the 
sperma took place by all the apertures simultaneously. My 
observations on the development of Borlasva olivacea agree, 
as far as they have been made, with those of Mr. MacIntosh. 
Circumstances have prevented me from carrying on con- 
tinuous series of experiments on the development of other 
species where the more interesting Pilidium larva makes its 
appearance in the eyolutional cycle. 
March, 1875. 
1 The appearance sometimes presented in Borlasia olivacea as if they 
lay independently behind the ganglia, must probably be ascribed to an 
abnormal tension under compression, the elastic tissue so constantly dis- 
tributed along with the nervous permitting of this separation for a short 
time; similar disjunction was never observed in the Mediterranean species, 
