Kingsley.] 
444 
[March 15, 
epithelial cells. The tail, however, affords good optical sections, 
the epiblast alone not well exhibiting cellular structure. In the 
centre of the tail can be seen the large cells of the notochord 
extending nearly to the tip of the tail. Above it extends a single 
layer of cells, much smaller in size, which are the homologues of 
the medullary cord of the higher vertebrates, while beneath may 
be seen a thicker layer of still smaller cells which must be 
regarded as the morphological equivalents of the hypoblast. 
Thus prematurely released from its proper envelopes this embryo 
soon died. 
A slightly later stage in its normal condition is represented in 
fig. 10. The tail continues to grow until it acquires length enough 
to entirely reach around the anterior portion of the embryo. 
Correlated with this lengthening of the tail is the formation of 
the “ eye.” The exact method of formation of this organ I do 
not know as it only becomes visible after the deposition of pig- 
ment in the cells. It appears at first as a round dark spot on or 
near the surface of the anterior or larger portion of the body and 
gradually grows darker with the development of the embryo. 
This “eye-spot” is single and by a study of its position in later 
stages we see that it has some close connection with the central 
nervous system. 
Soon after the appearance of the eye-spot certain changes can 
be indistinctly seen on the interior but not sufficiently clearly to 
be described. At the same time the perpheral portions of the 
body exhibit a tendency to clear themselves and become translu- 
cent, while the central portion remains opaque. At the anterior 
end the granules, which were the cause of the former opacity, seem 
to unite into a smaller number of larger globules. The tail at 
the same time is undergoing a degeneration which finally results 
in a breaking down of neural and enteric layers and eventually 
of the chorda dorsalis itself. At this time the embryo hatches 
and begins its free life. In what method the egg membrane and 
the avails of the ovarian pouch are ruptured I did not discover ; 
but the young on hatching pass out of the excurrent orifice of the 
parent. Their method of swimming strikingly resembles that of 
the Batrachian tadpole, which they also closely resemble in gen- 
eral appearance (fig. 11). The length ofthe free life from the 
