LEUCKART, ON DEVELOPMENT OF ECHINORHYNCHUS. 59 
unfrequently be seen to be propelled im different directions. 
The granular mass, moreover, itself lies free in the interior 
of this substance, and without any connection with the peri- 
pheral layer of parenchyma, as may be readily proved not 
only from the circumstance that it may be easily squeezed 
out of the embryo, but in a more direct manner from the 
fact that it is seen to change its place on the occurrence of 
any powerful peristaltic movement. 
During the first fourteen days after the commencement of 
its migration, the morphological development of the embryo 
undergoes no change. It merely increases in size, and this 
so rapidly that at the end of this period some individuals are 
met with measuring in length 0°6 and 0:7 mm., and having a 
transverse diameter of 0:15 mm. The embryo during all this 
time retains the spines at the anterior extremity, but the 
form of this extremity is so far changed that the dorsal sur- 
face above the vertex projects in the form of a transparent 
hemispherical eminence, which forms with the neutral sur- 
face an angle of about 100°, whose apex is constituted by 
the meeting of the two parallel longitudinal ridges above 
described. It is clear that the presence of these ridges 
interferes, to a certain extent, with the equable expansion of 
the anterior end of the body, and it is to this circumstance 
that is due the peculiarity of comformation of the anterior 
part of the head. The spines, hike the ridges, retain their 
former proportions and respective position. They are placed 
close to the longitudinal ridges on the sides of the cephalic 
surface, which bythis time has become raised into two rounded 
eminences. At this stage I have never observed any true 
boring movements, although the forepart of the body is still 
occasionally retracted. It would seem, nevertheless, as if the 
spines were still of some use in the locomotion of the embryo, 
affording it, as they do, the means of affixing itself. 
In consequence of this change of form of the anterior end 
of the body, the embryo has now acquired a more regular 
fusiform shape, which becomes more manifest when it has 
been rendered rigid and motionless by the endosmotic absorp- 
tion of water. 
But the growth of the embryo is not limited merely to the 
outer body. The nuclear granular mass in the interior has 
also considerably increased in size (in embryos of 0°7 mm. long 
to 0°09 mm.). Whilst at the same time it has lost its original 
granular aspect. Instead of the granules, pale cells are now seen 
measuring from 0:007 to 0°02 mm. im size, and continually 
multiplying. These cells constitute a compressed, almost 
spherical ball, with a well-defined outline. The.surrounding 
