960 REPORT—1896. 
AMMOCGTESs, 
In all figures the opereular appendage is marked out by its dotted appearance. 
holes, This glandular structure is not confined to the male scorpion, but is found 
also in the female, though not so well developed. 
So characteristic is the structure, so different from anything else, that I have no 
hesitation in saying that the thyroid of Ammoccetes is the same structurally as the 
thyroid of the scorpion, and that, therefore, in all probability the median projection 
of the operculum in the old forms of scorpions, such as Kurypterus, Pterygotus, 
Slimonia, &c., covered a glandular tube of the same nature as the thyroid of 
Ammoceetes, 
We see, then, that the structures innervated by the VIIth, IXth, and Xth 
nerves are absolutely concordant with the view that the primitive vertebrate 
respiratory chamber was formed from the mesosomatic appendages of such a form 
as Limulus by a slight modification of the method by which the respiratory 
apparatus of Thelyphonus and other Arachnids has been formed, according to 
acleod. The anterior limit of this chamber was formed by the operculum, the 
basal part of which formed a septum which originally separated the branchial from 
the oral chamber. 
Comparison of the Oral Chamber of Ammoceetes with that of Burypterus. 
Meaning of the Vth Nerve. 
Passing now to the oral chamber—zi.. to the visceral structures innervated by 
the Vth nerve—we find, as already suggested, distinct evidence in Ammoceetes of 
the presence of the modified prosomatic appendages of the original Eurypterus- 
like form. The large velar appendage is the least modified, possessing as it does 
the arthropod tubular muscles, a blood system of lacunar blood-spaces, and a 
surface covered with a regular scale-like pattern, formed by cuticular nodosities, 
similar to that found on the surface of Eurypterus and other scorpions. The 
velar appendages show, further, that they are serially homologous with the re- 
spiratory appendages, in that they have been utilised to assist in respiration, their 
movements being synchronous with the respiratory movements. 
