STRUCTURE AND DEVELOPMENT OF LOXOSOMA. 301 
Fig. 55 represents a larva after a free existence of about 
twenty-four hours ; the animal is seen from the ventral side, 
the ciliated ring being completely retracted into the vestibule, 
the narrowed opening of which is seen in the centre ( va ). By 
careful focussing could be made out the ciliary movements of 
the oesophagus and rectum, not indicated in the figure. The 
head or dorsal organ with its two eyes is very conspicuous and 
has in no way been altered in appearance by the production of 
the buds, which are seen as a pair of round projections at the 
sides of the dorsal organ, and at a level intermediate between 
it and the edge of the retracted vestibule. This position of 
the buds having been observed, it at once became obvious what 
was the nature of certain cells which had been repeatedly 
seen in the more advanced embryos within the brood pouch in 
exactly the position of the larval buds. These cells (fig. 57, b) 
form a group on each side, consisting of a small number of 
large rounded epiblastic cells lying at the sides of the brain, 
and between this organ and the ciliated ring. In larvae one 
or two days free they are found to be more numerous and form 
a considerable projection composed in the main of enlarged 
epiblast cells. In fig. 59, a horizontal section of a larva which 
had been free two days, one of the buds ( b ) is cut on the left 
side. It consists externally of a layer of very high epiblast 
cells. On the inner side of these cells occurs a large rounded 
mass which seems to contain only a single nucleus. This large 
cell in all probability belongs to the epiblast, which I have 
observed, from an examination of other larval buds, to give rise 
to a mass of cells which projects inwards, and no doubt 
eventually forms the lophophore and vestibule, in the same 
manner as in the buds developed by the adult. The section 
has passed through the eye of the opposite side, together with 
a portion of the corresponding half of the brain, and it is easy 
to see, from an inspection of this and other series of sections 
of larvae at the same or earlier stages, that the dorsal organ 
remains quite unaltered during the budding. 
In fig. 56 are represented two groups of cells ( hst .), appa- 
rently developed from the sides of the stomach. In larvae 
