On the other hand, it has been held that in these leeches there is no vascular system at all and that the entire system of spaces is coelom.
This sinus is continued round the oesophagus as the peri-oesophageal sinus, and thus the whole complex of the small arm-sinus has the relations of the so-called vascular system of a Sipunculid.
The root differs from the shoot in the characters of its surface tissues, in the absence of the green assimilative pigment chlorophyll, in the arrangement of its vascular system and in the mode of growth at the apex, all features which are in direct relation to its normally subterranean life and its fixative and absorptive functions.
The vascular system is highly developed (in the non-degenerate forms); large arterial branches closely accompany or envelop the chief nerves; capillaries are well developed.
With a few exceptions among the Polychaeta the vascular system is always present among the Chaetopoda, and always consists of a system of vessels with definite walls, which rarely communicate with the coelom.
The vascular system does not readily lend itself to morphological comparison between such widely different animals as Balanoglossus and Amphioxus, and the reader is therefore referred to the memoirs cited at the end of this article for further details.
The vascular system is not extensive, the arteries soon ending in the well-marked spongy tissue which builds up the muscular foot, parapodia, and dorsal body-wall.
Goodrich that the vascular system and the coelom are in communication (as in vertebrates by means of the lymph system).
In favour of regarding the vascular system as totally absent, is the fact that the median coelomic channels contain no dorsal and ventral vessel.
In the blade of a typical leaf of a vascular plantessentially a thin plate of assimilating tissuethe vascular system takes the form of a number of separate, usually branching and anastomosing strands.