and is not provided with valves. The upper portion 
is attached to the dorsum at intervals by suspensory 
fibres (muscular), so that a festooned appearance is 
given in longitudinal section. There is, however, no 
true division into compartments. Laterally large cells 
(pericardial cells) are arranged throughout its entire 
extent, and fibres of a muscular nature (alary muscle) 
pass from the body wall and end in branches in close 
connexion with the dorsal vessel. 
At the first abdominal segment the dorsal vessel 
dips down beneath the mesophragma, lying as it does 
so in direct contact with the cuticle. In the thorax 
it again arches upwards, and lies between the lower 
portions of the antero-posterior wing muscles close 
above the anterior portion of the mid-gut. 
In the anterior third of the thorax it divides 
into two smaller portions which pass outwards, and 
coming in contact with the salivary ducts enter the 
neck. 
Blood spaces without definite walls occur through¬ 
out the body. The thorax especially contains large 
spaces among the muscles, and the complex fat-body 
which lies between and supports the organ is every¬ 
where bathed with blood fluid. 
The Reproductive System 
The organs of the reproductive system are :— 
1. Ovaries. 
2. Oviducts and common oviduct. 
3. Mucus gland and duct. 
4. Spermathecae and ducts. 
The ovaries occupy a variable position dependent 
upon the state of their development. In the newly- 
hatched mosquito they are small bodies lying in the 
