302 =Prof. Miailand Mr. R. Shelford on the Structure and 
small size of the dorsal vessel and the rapidity with which 
the cords break up. We have observed that during dis- 
integration very minute filaments, or rods, project from 
the cord, as if they were about to become free and form 
some constituent of the blood. The nuclei also become 
free and escape into the blood, as we infer from their fre- 
quent occurrence at the critical stage in a nearly detached 
condition. In a young pupa the cords are almost the same 
as in the larva,while in a pupa approaching the time of final 
transformation, not a trace of the cords is to be found. 
The observations next to be related may throw some 
light upon the nature of the cellular cords. 
In a young larva there was seen, just in front of the 
rectum and close to the anus, a multicellular, vacuolated 
body of rounded, irregular form, which seemed to be 
continuous with the epidermis, to which it was attached 
by a narrow stalk, Similar bodies have been found pro- 
jecting from the dorsal surface. ‘They all le in the body- 
cavity (hematoccel). Segmentally arranged and single 
cenocytes occur throughout the body of the larva. They 
are often attached by threads or stalks to the body-wall, 
and when disintegrating have been observed to give off 
many fine filaments, which perhaps pass into the blood, 
The nuclei are of enormous size, and contain many 
nucleoli. The protoplasm of the cenocytes includes a vast 
number of granules or corpuscles, with occasional vacu- 
oles. . A peripheral nucleus is sometimes found (fig. 52). 
We have not been able to find a close parallel 1 to the 
cellular cords in any other insect. Outside the class of 
insects we can only point to rather vague and distant 
analogies, such as the following :— 
Certain Oligochzet worms possess organs which have 
been called cardiac bodies and blood-glands.* 'The Enchy- 
traeidze sometimes possess a cellular rod which runs the 
whole length of the dorsal vessel, being attached to its 
ventral wall. Michaelsen, the discoverer of the struc- 
ture, assigns to it a mechanical function, that of facili- 
tating occlusion of the tube during systole, without 
extreme contraction of the wall of the vessel. It has 
been suggested, though apparently not proved, that this 
cellular cardiac body of the Enchytrzeidz originated in a 
so! Megane ian of the fe sopnage If this is well- 
* Beddard, Molen of the Order Oligocheta, p. 77. 
