028 GEOFFREY SMITH. 
3. Inrernan Anatomy (Anaspides tasmanie). 
(4) Pericardium, Heart and Vascular System. 
If a median dorsal incision be made in Anaspides, and the 
skin and dorsal muscles be turned away on each side, we 
find that we are in a spacious division of the body cavity with 
a very definite pigmented floor, which stretches from the 
first to the last segment. ‘This space is the pericardium and 
its floor is pierced laterally in each segment by lacunar 
spaces which lead down into the cavities surrounding the 
bases of the appendages. ‘he heart, which les in the peri- 
cardium, is a long contractile tubular structure with an 
anterior expanded portion stretching from the first to the 
eighth thoracic segment ; in the first abdominal segment it 
narrows considerably and is continued into a vessel which 
appears to be contractile, but is perhaps more rightly to be 
considered as a posterior dorsal aorta. The heart and aorta 
are fixed to the floor of the pericardium by a series of inter- 
segmental short muscles, while the heart in the thoracic 
region is also supplied with segmental dorsal alary muscles. 
The heart is constricted interseementally where the ventral 
muscles attach it to the floor of the pericardium, but ostia 
are only present in one place, namely at the base of the 
third thoracic segment, where there appears to be a single 
pair. 
Anteriorly the heart gives off three arteries, a median 
ophthalmic artery and paired antennary arteries. 
In the seventh thoracic segment a sternal artery leaves 
the heart, and running obliquely downwards enters a ventral 
artery in the sixth thoracic segment, which runs forwards and 
backwards just dorsal to the nerve cord (text-fig. 44, art. 
vent.). A small subneural vessel is also present. 
The elongated tubular heart is of a strictly Peracaridan 
type, and recalls very strongly the heart of the Myside; the 
arterial system is of a generalised Malacostracan nature. 
The dorsal muscles which form the roof of the pericardium 
