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 Aminoccetes 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 palteo- 

 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 Ammocuetes. 



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 Ammoccotes 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 Ammocoetes there should still exist the 

 remains of a tube extending from the IVth ventricle to the surface at 

 the conns post-eommismralis, which can actually be traced right into 

 this tissue on the outside of the brain (see Fig. 13, a-e, PI. XXVI., 

 in my paper in the Quarterly Journal of Microscopical Science). 



