Blood Vessels –
The blood vascular system includes three main blood vessels and many assisting blood vessels which are as follows-
Main blood vessels :
- Dorsal BV –
It is found in complete body length mid-dorsally to the alimentary canal. It appears to be a dark line from the outside. It’s walls are thick, muscular & contractile. Hence, the dorsal B.V. functions like a heart.
It is provided with valves and there is a pair of valves in each segment The blood in the dorsal BV flow’s from posterior to anterior direction.
It acts as collecting BV from last to 14th segment and in the first thirteen segments, it acts as distributing B.V. In first thirteen segments, it supplies blood to the alimentary canal & reproductive organs found in these segments. From last to 14th segment, it collects blood from the body wall, intestine, reproductive organs & subneural B.V.
- Ventral blood Vessel –
It is situated mid-ventrally to the alimentary canal from 2nd to last body segments. It is thin-walled, less muscular & non-contractile and it is without valves. The blood flows from forward to behind.
It acts as a distributing blood vessel in the whole body length. It provides blood to the body wall & to the integumentary nephridia. It also supplies blood to the intestine, septa, septal nephridia & reproductive organs in 14th to last segments.
- Lateral-oesophageal and Sub-Neural blood Vessel –
Sub neural BV is found mid-ventrally just below’ the alimentary canal from 14th to last segments. It is thin-walled, non-muscular & non-contractile blood vessel which is without valves.
The blood in the sub-neural BV flows from forward to behind & it acts as a collecting B.V.
In 14th segment, the sub-neural BV bifurcates to form two lateral oesophageal blood vessels. They are situated on both the sides of the alimentary canal in first thirteen segments.
The lateral oesophageal BVs. collect blood from the organs found in first thirteen segments. The blood flows from forward to behind.
Accessory Blood Vessels :
The blood vascular system has following accessory blood vessels-
- Supra-gastric or Supra-oesophageal BV –
It is a small blood vessel which is found in 9th to 14th segments just above the stomach. It collects blood from the stomach. The blood flows from forward to backward.
- Ring Vessels –
There are 6 pairs of small ring vessels which are found in the wall of the stomach. They collect blood from the stomach & carry it into the supra-gastric B.V.
- Anterior loops –
There are 2 pairs of anterior loops which are found in 10th & 11th segments. They connect both the lateral- oesophageal blood vessels to the supra-oesophageal B.Vs. The anterior loops are without loops & are non- contractile.
- Hearts –
It has four pairs of hearts which are tubular & non- contractile. They are found in 7th, 9th, 12th & 13th segments. The hearts of the 7th & 9th segments are called as lateral hearts. They connect dorsal BV to the ventral BV. Each lateral heart has 4 pairs of valves. The hearts of 12th & 13th segments are called as latero- oesophageal hearts. They connect dorsal BV & supra- oesophagel BV to the ventral BV. Each heart has 3 pairs of valves.
- Commissural BV –
There is a pair of commissural B.Vs. in each segment from 14th to last segment. They connect sub-neural BV to the dorsal BV. Each commissural B.V gives out a small septo-intestinal B.V. which supplies blood to the septum & the intestine.
- Ventro-tegumentary BV –
The ventral BV gives out a pair of ventro-tegumentary BV in each body segment. They supply blood to the body wall & integumentary nephridia of the same segment. The blood from these parts is collected by the dorsal B.V.
- Ventro-intestinal & Dorso—Intestinal B.Vs. –
The ventral B.V. gives out one ventro-intestinal B.V. in each segment from 14th to the last segment. It supplies blood to the intestinal wall. In the intestinal wall, it forms two blood pluxes viz.— outer intestinal plux & inner intestinal plux. Both the pluxes remain connected to each other. The blood from the intestinal wall is collected by dorso-intestinal B.Vs. Each segment has 2 pairs of dorso-intestinal B.Vs.
