966 REPORT—1896, 
Comparison of the Pituitary Gland with the Coxal Gland of Limulus. 
In connection with the second ccelomic cavity in Limulus is found an ancient 
gland, partially degenerated according to some views, which was probably excretory 
in function and has been considered as homologous to the crustacean green glands. 
In a precisely corresponding position, and presenting a structure fairly similar to 
that of the coxal gland of Limulus, we find in Ammoccetes and in other vertebrates 
the pituitary gland. How far this gland tissue is developed in connection with 
the mandibular head cavity I do not know, but I venture to suggest that the 
complete evidence of its homology with the coxal gland will be found in its 
developmental connection with the walls of the 2nd or mandibular head 
cavity. 
Comparison of the Vertebrate Heart and Ventral Aorta with the Ventral 
Longitudinal Branchial Sinuses of Limulus and its Allies. 
The heart of the vertebrate presents two striking peculiarities, which make it 
different from all invertebrate hearts: first, its developmental history is different; 
and, secondly, it is at first essentially a branchial rather than a systemic heart. 
The researches of Paul Mayer ! have shown that the subintestinal vein, from which 
in the fishes the heart and ventral aorta arise, is in its origin double, so that in all 
vertebrates the heart and ventral aorta arise from two long veins which are 
originally situated on each side of the middle line. By the formation of the head 
fold these come together ventrally, coalesce into a single tube to form the 
subintestinal vein and heart, still remaining double as the two ventral aortz 
with their branchial branches into each gill, as is well shown in the case of 
Ammoceetes. 
It is a striking coincidence that in Limulus and the Scorpions two large 
venous collecting sinuses are found situated in the same ventral position, for the 
same purpose of sending blood to the branchiw, as already described for the 
vertebrate ; still more striking is it to find, according to the researches of Milne 
Edwards and Blanchard, that these longitudinal sinuses have already begun to 
function as branchial hearts, for they are connected with the pericardium by a system 
of transparent muscles, described by Milne Edwards and named by Lankester veno- 
pericardiac muscles. These muscles are hollow, both near the vein and near the 
pericardium, so that the blood in each case fills the cavity, and, as they contract 
with the heart, that part of them in connection with the venous collecting sinus 
already functions, as pointed out by Milne Edwards and Blanchard, as a branchial 
heart. 
By this theory, then, even the formation of the vertebrate heart is prevised in 
Limulus, and I venture to think that in Ammoccetes we see the remnant of the 
old dorsal single heart of the arthropod in the form of that peculiar elongated 
organ composed of fattily degenerated tissue which lies between the spinal cord 
and the dorsal median skin. 
Comparison of the Cuticular and Laminated Layers of the Skin of 
Ammocetes with Chitinous Layers. 
The external epithelial cells of Ammoccetes possess a remarkably thick cuticular 
layer. The striated appearance of this layer is due to a number of pores through 
which the glandular contents of the cells are poured when the surface is made to 
secrete. That this striated appearance is due to true porous canals, just as in 
chitin, and not to a series of rods, is easily seen by the inspection of sections, and 
also by watching the secretion through them of rose-coloured granules when the 
living cell is stained with methylene blue. The surface layer of this cuticular 
layer, according to Wolff, resists reagents in the same manner as chitin. 
» Mayer, Mitth. a. d. Zool. St. zu Neapel, vol. vii. 
2 Wolff, Jen. Zeitsehr. vol. xxiii. 
