20 
Siphonophora Rosarum 
arising from each stigma and dividing into dorsal and ventral branches 
(Plate I, Figs. 22 and 23). 
The dorsal tracheal system. The dorsal branches (Text Fig. 13), 
when given off from the main trachea, pass along under the latero- 
dorsal surface of the body to a position about two-thirds of the way 
between the lateral and the dorso-medial lines. In this position, each 
Fig. 13. The Dorsal Tracheal System. (x 46.) 
abd. st. 1—7 = stigmata of the 1st—7th abdominal segments. ant. = antenna. 
cor. = cornicle. e. = eye. It. d. conn. = left dorsal connecting trachea. 
th. st. 1 and 2 —1st and 2nd thoracic stigmata. 
branch, with the exception of the first thoracic, divides again into two, 
and the branches join up to form a single longitudinal trachea (d. conn.) 
(the Langsstamme of Witlaczil) on each side of the dorso-medial line, 
extending from the first thoracic segment to the seventh abdominal 
segment. The course followed by this longitudinal connective trachea 
is a zigzag one, owing to the subdivisions of the dorsal tracheae meeting 
at an angle. From each of the long tracheae—one on each side of the 
median dorsal line—small ramifications are given off into the space 
enclosed by them. These branches pass downwards and aerate the 
organs in their immediate vicinity. The right and left divisions of 
