Question

In Earthworm, dorsal blood vessel is collecting channel
A. Behind $\mathop {13}\nolimits^{th}$ segment
B. Anterior to $\mathop {13}\nolimits^{th}$ segment
C. Throughout
D. In typhlosolar region

Answer 1

Earthworm belongs to kingdom Annelida. Dorsal blood vessels are usually dark brownish and reddish in appearance. It runs towards the top of the intestine in earthworms. First circulatory blood flows in ventral blood vessels then the blood is returned to the capillary bed and then to the dorsal blood vessel which finally goes into the aortic arch.

Complete answer:
Dorsal blood vessel: It is the largest blood vessel of the body running mid-dorsally above the alimentary canal, from one end of body to the other. It has valves which prevent the backflow of blood It receives blood from various parts of earthworm through different connecting vessels. As it runs above the intestine. Intestine runs from $\mathop {15}\nolimits^{th}$ segment and runs behind $\mathop {13}\nolimits^{th}$segment above the intestine.
Now let us match this with given options
Behind $\mathop {13}\nolimits^{th}$ segment: - as the dorsal blood vessel runs above the intestine so it runs behind $\mathop {13}\nolimits^{th}$ segment. Thus, this option is correct.
Anterior to $\mathop {13}\nolimits^{th}$ segment :- commissural blood vessels runs anterior to $\mathop {13}\nolimits^{th}$ segment and not dorsal blood vessel. Hence this option is not correct.
Throughout: - these vessels run only above the intestine as the intestine runs after $\mathop {15}\nolimits^{th}$ segment so it will not run after that. Thus, the option is wrong.
In typhlosolar region: - it is special feature of intestine and not circulatory system and runs between $\mathop 9\nolimits^{th}$ and $\mathop {25}\nolimits^{th}$ segment. Thus, this option is not correct.

Our required answer is A) behind $\mathop {13}\nolimits^{th}$ segment.

Note:
In earthworms, there are four pairs of tubular hearts. The anterior two pairs of hearts known as lateral hearts lie in the $7{\text{ }} and {\text{ }}9$ segments. They connect the dorsal blood vessel with the ventral blood vessel. The posterior two pairs of hearts are called latero-oesophageal hearts and are situated in the $12$ and $\mathop {13}\nolimits^{th}$ segments.