620 PROFESSOR E, RAY LANKESTER. 
ing part of the vascular system in Limulus, with its nerve- 
ganglion collar, cord, and main nerves, was first observed by 
Owen (‘ Lectures,’ 1855), but has been fully demonstrated and 
described in detail by Milne-Edwards. The supra-spinal 
artery of Scorpio is represented by a complete arterial invest- 
ment of the nerve-ganglion collar, including the brain, and of 
the chief nerves, as well as of the ventral nerve-cord arising 
from it, so that the nerves actually lie izszde arteries and the 
brain, nerve-collar and nerve-cord are placed in the interior 
of a great arterial trunk corresponding to the supra-spinal 
artery of the Scorpion. 
The agreement of these parts in Limulus and the Scorpion 
has been insisted upon by M. Milne-Edwards at page 19 of 
his memoir (8). 
No Crustacean presents so complete a vascular system as 
Limulus, nor can we find anywhere but in Scorpio an artery 
originating by arterial arches embracing the cesophagus and 
passing through the body in close association with the nerve- 
cord as a main channel for the distribution of the blood. 
The chief difference (by no means a small one) between 
this part of the arterial system in Limulus and Scorpio is 
that the arteries to the cephalothoracic limbs and brain are 
in the former given off from the cesophageal vascular collar, 
or from its united factors, whilst in Scorpio they originate 
from a distinct trifurcate anterior continuation of the dor- 
sally placed truncus arteriosus (see woodcut, fig. 19). 
§ e. GENERATIVE GLANDS.—The position of the exter- 
nal openings of the generative organs has already been 
shown to correspond exactly in Limulus and Scorpio, being 
placed in both in the segment next following that to which 
the sixth pair of leg-like appendages are attached, and being 
covered in by an opercular plate with a bifid margin, the 
plate being formed by the coalescence of the two appendages 
proper to this segment. 
Limulus and Scorpio agree in having the sexes distinct. 
They also agree in the general form and character of the 
ovaries and testes respectively, and in the fact that the 
ovary and the testis are in fundamental form like to one 
another. 
Though it might be possible to find an ovary or a testis 
similar in form to those of Limulus and Scorpio among Crus- 
tacea (I do not know of one), yet it is an important fact, as 
part of our cumulative evidence of affinity between the two, 
that in both these animals the ovaries and the testes present 
the same characteristic form, and that that form is an unusual 
