THE EVIDENCE OF THE THYROID GLAND 209 
THE GENERATIVE GLANDS OF LIMULUS AND ITS ALLIES. 
The whole argument, so far, has in every case ended with the 
conclusion that the original scorpion-like form with which I have 
been comparing Ammoccetes resembled in many respects Limulus 
rather than the present-day scorpions, and therefore in the case also 
of the generative organs, with which the thyroid gland or paleo- 
hysteron was in connection, it is more probable that they were 
cephalic in position rather than abdominal. If this were so, then 
the duct on each side, starting from the median ventral uterus, would 
take a lateral and dorsal course to reach the huge mass of generative 
gland lying within the prosomatic carapace, just as I have repre- 
sented in the figure of Eurypterus (Fig. 79), a course which would 
take much the same direction as the ciliated groove in Ammoccetes. 
We ought, therefore, on this supposition, to expect to find the 
remains of the invertebrate generative tissue, the ducts of which 
terminated in the thyroid, in the head-region, and not in the 
abdomen. 
Upon removal of the prosomatic carapace of Limulus, a large 
brownish glandular-looking mass is seen, in which, if it happens to 
be a female, masses of ova are very conspicuous. This mass is com- 
posed of two separate glands, the generative glands and the hepatico- 
pancreatic glands—the so-called liver—and surrounds closely the 
central nervous system and the alimentary canal. From the genera- 
tive glands proceed the genital ducts to terminate on the posterior 
surface of the operculum. From the liver ducts pass to the pyloric 
end of the cephalic stomach, and carry the fluid by means of which 
the food is digested, for, in all these animals, the active digesting 
juices are formed in the so-called liver, and not in the cells of the 
stomach or intestine. 
It is a very striking fact that the brain of Ammoccetes is much 
too small for the brain-case, and that the space between brain and 
brain-case is filled up with a very peculiar glandular-looking tissue, 
which is found in Ammocoetes and not elsewhere. Further, it is also 
striking that in the brain of Ammoccetes there should still exist the 
remains of a tube extending from the Vth ventricle to the surface at 
the conus post-commissuralis, which can actually be traced right into 
this tissue on the outside of the brain (see Fig. 13, a-e, Pl. XXVL., 
in my paper in the Quarterly Journal of Microscopical Science). 
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