Question

__ heart of cockroach chamber is without ostia.
A. 1st prothoracic
B. Last thoracic
C. First abdominal
D. Last abdominal

Answer 1

Hint: The heart of cockroach consists of thirteen contractile chambers. A pair of apertures called ostia which are present laterally at the posterior end of each chamber.

Complete answer
As you can see in the question, the cockroach's heart chamber is without ostia. First of all, what is ostia?
The heart of cockroach consists of thirteen contractile chambers. A pair of apertures called ostia which are present laterally at the posterior end of each chamber. Each chamber of the heart receives oxygenated blood from the dorsal sinus through ostia. Ostia are guarded by auricular valves to check the flow of blood from the heart to the pericardial sinus (blood filled space).

Our 1st option is 1st prothoracic.
The thorax of cockroaches is divided into 3 parts: prothorax, mesothorax and metathorax.
In Cockroach we find a tubular heart mid-dorsally situated with ten chambers in the abdominal region and three in the thorax region and in 1st prothoracic region ostia is not found.

Our 2nd option is last thoracic which means metathoracic region. As we know, 3 chambers of the heart present in thorax with two ostia in mesothorax and metathorax. So, the last thoracic chamber i.e. metathorax has ostia. So, this option is not correct.

Option C. Is first abdominal. As we know all the chambers of the cockroach heart in the abdomen have ostia. So, the first abdominal has an ostia.

Option D is the last abdominal. As we already mentioned that all chambers of the abdomen have ostia. So, this option is also wrong.

So, the correct option is A. 1st prothoracic

Note: Cockroaches have 13 chambered hearts. 3 chambers are present in the thorax and 10 in the abdomen. All chambers of thorax except prothorax and all chambers of abdomen have ostia.