278 
MR. NEWPORT ON THE NERVOUS AND CIRCULATORY SYSTEMS 
In the next family, the Polydesmidce (fig. 1 7 ), the circulatory system closely resem- 
bles that of the Iulidae. Thus there are the same divisions of the heart into cham- 
bers, which distribute systemic arteries, and the aortic arches are given off a little 
behind the head. But the development of most of the structures is more complete. 
There are fewer segments to the body, and chambers to the heart, and the latter 
are more muscular and distinct. The spinal vessel now forms a single large canal 
above the nervous cord, giving off fewer branches, but it still exhibits the remains of 
its original formation from aggregations of nucleated cells, which are distinct in its 
texture, but less so than in the corresponding structure in lulus. 
In the Glomeridce the development is still more complete, and approaches in its 
general condition to that of the Crustacea. 
In the Geophilidce, the lowest of the Chilopoda, which still retain the general ver- 
miform type of the Chilognatha, the segments of the body and the chambers of the 
heart are more numerous even than in the Iulidae. But the whole organization of 
this family is greatly in advance of the lulus. The heart presents a greater number 
of segments than in any other Myriapodes. In some species, as in Mecistocephalus 
maxillaris, Gervais*, there are only forty-six chambers, but in others, as in Goni- 
bregmatus, Newport, there are more than three times that number, or at least one 
hundred and sixty. Yet notwithstanding this multitude of parts and segments, the 
whole organ and its vessels are further developed than in the Chilopoda. The cham- 
bers are divided by more distinct valves, and give off each but one pair of vessels. 
The aortic arches are a single pair, as in Scolopendra, and the supra-spinal artery is 
not so large as the nervous cords, but is a distinct vessel that gives off a few lateral 
branches, as we shall find in the next family. 
In the Scolopendridce there is a still more perfect development of the whole of these 
structures. The heart (figs. 18, 19, 20, 21, 22) is inclosed in a distinct membranous 
covering, which may be regarded as a true pericardium. It is also separated from 
the great mass of fatty omentum by which it is surrounded, and from the organs of 
generation, and the alimentary canal, which are situated beneath it, by a distinct, 
thick peritoneum, which entirely invests the alimentary canal, and in which a great 
number of circulatory vessels ramify and anastomose. The pericardium that incloses 
the heart is a loose, delicate membrane, between which and the sides of each cham- 
ber there is a slight interspace. It was regarded by Straus Durckheim as an auricle. 
It is attached to each chamber along the median line, both on the upper and under 
surface of the organ. At its sides it is reflected downwards and outwards, and has 
lateral prolongations that pass between the ala cordis, and seem to inclose vessels 
that return the blood to the heart. The number of chambers (1 to 21) is reduced in 
the heart of the Scolopendra to twenty-one, the anterior (1.) and posterior (21.) of 
which are the shortest and smallest. This number is uniform throughout the whole 
of the species, and the structure and distribution of the parts in all are very similar. 
In Scolopendra alternans, Leach, and S. Hardwicltei, Nob., there are two short and 
* This authority refers only to the specific name. 
