Dorsal blood vessel

• It is the principal blood conducting organ in insects which remain closed at the posterior end and opens anteriorly in to the head.
• It is divided into an anterior aorta and posterior heart extending throughout the length of the body.

1. Aorta: It is the anterior part of the dorsal blood vessel and functions as principal artery. It is present in the thoracic region and opens in to the head near the brain. Its attachment with the heart posteriorly is marked by an aortic valve. Anteriorly sometimes it gets divided into 2 or more cephalic arteries in the head.

2. Heart: It is the posterior part of dorsal blood vessel extending up to the terminal end of the abdomen. Heart remains in position with the help of alary muscles that are attached to the tergum of the abdomen on one side and to the dorsal diaphragm on other side.

• Heart consists of number of chambers marked by constrictions and the presence of the opening called the incurrent ‘ostia’ which allow the entry of blood from pericardial sinus in to the heart.
• The number of ostia depends upon the number of heart chambers which will be usually 9. The walls of heart also consists of muscles. Heart mainly functions as the pumping organ in to the aorta.

Accessory pulsatile organs:

• Insects consists of sac like structures called accessory pulsatile organs, which are present at the base of the appendages such as wings, legs and antenna.
• They pulsate independently and supply adequate blood to the appendages.