MICHIGAN ACADEMY OF SCIENCE. 
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development and remain in a more or less primitive condition for some 
time. They then migrate by self active amoeboid movements or by a 
passive displacement due to the shifting and readjustment of embryonic 
tissues during development to the definitive position in the sex glands. 
This view is supported by many investigators who have succeeded in 
tracing their origin to embryos in blastoderm stages, but who have not 
as yet determined their origin because of the difficulty in distinguishing 
the germ cells from somatic cells in still earlier stages. It seems prob- 
able however, that they are really present in these earlier stages al- 
though no methods have yet been discovered by means of which they 
can be recognized. 
The material upon which the present investigation is based, consists 
of embryos of the toadfish, Opsanus tan, a marine Teleost belonging to 
the family Batrachidae. This species occurs abundantly along our east- 
ern coast, and because of its peculiar habit of nesting in such recep- 
tacles as tin cans and rubber boots, and also under stones and boards, 
has been a subject of much interest and study. The eggs after being 
laid adhere to the inside surface of the receptable or on the under sur- 
face of the stone or board and remain attached until the young are 
about three-fourths of an inch in length. The fry then break loose 
from the adhesive disc and escape thru a rupture of the egg capsule into 
the outside world.* 
While at the Marine Biological Station, Woods Hole, Mass., during 
the summer of 1911' a complete series of embryonic stages of the toad- 
fish was obtained. The material was fixed in various solutions includ- 
ing Bouin’s picro-formol, Tellyesnicky’s and Zenker’s fluids. These fixa- 
tives proved satisfactory but the great amount of yolk present in this 
egg became so hard that it was necessary to remove the blastoderm be- 
fore sectioning the embryo. Serial parafin sections six microns in thick- 
ness were cut transversely and longitudinally and stained in most cases 
with two percent acid haemalaun and counterstained with Orange 
G. or eosin. The series were studied beginning with the oldest embryos 
and then proceeding in succession to younger stages. 
In embryo number 105Ab, which measures 8.0 mm. in length, and 
still retains a large yolk sac, most of the germ cells occupy their defi- 
nitive position in the sex glands. These glands extend as longitudinal 
ridges or evaluations of mesothelial tissue projecting into the body 
cavity one on either side of the dorsal mesentery of the alimentary 
canal. The germ cells are easily seen in sections and are distinguished 
by their large size, circular outline, and well defined nucleus and nuc- 
leolus. The above characteristics have been the main features for 
recognizing the germ cells in early stages of both Vertebrates and In- 
vertebrates. 
No attempt has been made as yet to count the number of germ cells 
in the toadfish, but it was noticed that they are about evenly distributed 
between the two sex glands. 
Figure I is from a micro photograph of a portion of a cross-section 
of enibyro 105Ab thru the region of the sex glands. 
Figure 2 shows a small portion of Fig. 1 more highly magnified. 
*For fuller description of the habits of the toadfish, refer to E. W. Gudger’s account on the ‘‘Hab- 
ts and Life History of the Toadfish (Opsanus tau).” Bulletin Bureau of Fisheries, Vol. 28, 1908. 
