“THE DEVELOPMENT OF ASTERINA GIBBOSA. 371 
The History of the Young Star-fish. 
The just metamorphosed Asterina gibbosa has a disc of 
about ‘6 millimetre in diameter; if we take R to denote the 
length from the tip of the arm to the centre of the disc, then 
R equals ‘36 millimetre. A larva such as that figured in 
figs. 51—53 may be ‘8 millimetre from the tip of the adhesive 
disc to the posterior end, and measured obliquely from the 
dorsal end of the preoral lobe may exceed a millimetre in 
length. There is, therefore, a considerable diminution in size 
during the metamorphosis, the reason of which is evident when 
we consider that no nutriment is taken during this time. A 
full-grown specimen may have a diameter one hundred times 
greater than that of the just metamorphosed star-fish,—that is, 
it may exceed the latter one million times in bulk. The young 
star-fish, however, rapidly increases in size, and by the time 
R equals 3:7 millimetres the ovaries are visible. This is the 
oldest stage I have examined; my account of the histology is, 
however, taken from smaller specimens, in whichRequals ‘8mm. 
The changes we shall have to consider are (1) the formation 
of the primitive germ cells, the ovoid gland, genital rachis, and 
ovaries ; (2) the dermal branchie; and (3) general histological 
differentiation. 
We have already in Fig. 76 seen the first trace of the ovoid 
gland. It there appears as a ridge projecting into the axial 
sinus ; inside this ridge there is as yet to be found only ameebo- 
cytes, jelly and fibres, as is the case with the other blastoceelic 
spaces in the larva. Later, a thickening of peritoneum takes 
place on the wall of the left posterior ccelom opposite the aboral 
end of this ridge—and from this thickened patch a cord of cells 
grows into the ridge, gradually forcing its way in an oral 
direction ; this is the characteristic core of the ovoid gland. 
From this same thickening of peritoneum a cord of cells 
grows out in a direction parallel to the disc ; this is the origin 
of the genital rachis. By the outgrowth of a flap of peritoneum 
it is enclosed in a space which is called the aboral sinus. The 
genital rachis and the space enclosing it both give off branches 
VOL. 38, PART 3.—NEW SER. BB 
