60 LEUCKART, ON DEVELOPMENT OF ECHINORHYNCHUS. 
parenchyma, as at an earlier period, consists of a fine granular 
substance, of nearly fluid consistence, out of which, moreover, 
on prolonged contact with water, numerous clear drops 
about 0°38 mm. in diameter exude, which at first present a 
perfectly homogeneous aspect, but, subsequently, in conse- 
quence of their undergoing a sort of coagulation, exhibit a 
regular nucleus of considerable size (0'016 mm.), and strongly 
refractive power. That these bodies, notwithstanding their 
celleform structure, are not a normal constituent of the 
embryonal body, is clearly manifest from the circumstance 
that they may be seen gradually forming during the exami- 
nation, and disappearing as soon as the object is floated in a 
thin solution of albumen—a proceeding which it is advisable 
to adopt upon other grounds as well. 
The peripheral layer of contractile substance still retains 
its former condition, except that, of course, it has increased 
in thickness, and become more sharply defined on its inner 
surface. Its greatest thickness is still, as before, towards the 
anterior end of the body, although the knob-like projection 
has in the meanwhile disappeared. 
After the embryo has attained the dimensions just stated 
without any other essential change, it begins, in the course 
of the third week, to exhibit a most wonderful metamor- 
phosis. The nucleus, which up to this time has been constituted 
“of a simple, small aggregation of cells, now increases rapidly 
in size, and at the same time elongates, and becomes trans- 
formed by a definite grouping of its elements into a complex 
organism, in which, after a short time, may indubitably 
be recognised the features of a young Echinorhynchus. 
During this process, however, the body of the embryo 
remains unchanged, except that it is slightly larger (up to 
0:09 mm.), and presents, in the cortical layer, yellow granules 
constantly increasing in number, and which necessarily offer 
no slight obstacle to the further study of the processes 
going on in the interior. 
The embryo of Echinorhynchus, therefore, stands in the 
same relation to the future worm that the Pluteus does to 
the Echinoderm or the Pilidium to Nemertes. As in those 
cases, so in Echinorhynchus, the ultimate animal arises in the 
interior of the primordial body, by a process which presents 
so close an analogy with the production of an embryo, and, 
consequently, with the act of generation, that one feels inclined 
at once to identify it with such an act, and, consequently, 
to regard the Kchinorhynchus as exhibiting, instead of 
a metamorphosis, an alternation of generations in its mode of 
development, 
