LIMULUS AN ARACHNID. 617 
and then penetrates the heart. From the heart, the dimen- 
sions of which are considerable, it is forced into the tubular 
arteries with resisting walls, the distribution of which is 
exceedingly complex, with frequent anastomoses, whilst their 
terminal ramifications, which are of marvellous tenuity and 
abundance, can be followed into the substance of the most 
delicate membranes.” ‘These capillaries are figured by M. 
Milne-Edwards, but we have not of them, any more than of 
the tissues of Scorpio, a satisfactory histological account. 
Gegenbaur (2), whose observations were made on spirit speci- 
mens, did not observe these finer ramifications of the vessels, 
but supposed the arteries to lead into intercommunicating 
lacunee without definite walls. 
As to Scorpio, it may be justly said that it was the main 
purport of Newport’s memoir to make known just such an 
extended vascular system in the Myriapoda and Arachnida 
as above indicated for Limulus, though M. Alphonse Milne- 
Edwards does not cite Newport’s work, but unjustly appeals 
to the second-hand authority of M. Blanchard, for the few 
facts which he mentions relative to the Scorpion. And 
further, the general description of the circulation above 
given as to Limulus is strictly applicable as a summary of 
Newport’s observations upon the course of the blood and 
distribution of the vessels in the Scorpion. 
Newport’s description and figures of the heart and its 
main arteries in Scorpio show a close agreement with these 
parts in Limulus, as described by Milne-Edwards. A revi- 
sion of these structures in the Scorpion, in the light of what 
is now known as to Limulus, would probably show a still 
closer agreement in some details, especially were injection 
practised upon freshly killed specimens. 
The diagrams here given will enable the reader to judge 
of the general features of the arterial system in the two 
animals. 
The heart of both Limulus and Scorpion is an elongated 
organ, constricted so as to form eight successive chambers, 
which are imperfectly marked in the Limulus, but more 
obvious in the Scorpion, since in that animal imperfect 
transverse septa occur within it, less complete, according to 
Newport, than in other Arthropod hearts. In front of the 
eight chambers the heart is continued in both animals as a 
truncus arteriosus towards the head. Posteriorly it is con- 
tinued as a posterior aorta in Scorpio into the cylindrical 
tail; but in Limulus, in accordance with the reduction of that 
region of the body, it ends blindly. The eight chambers of the 
Scorpion’s heart appear to be the exact equivalents of the less 
