ECHINODERMS. 131 
lymphatics, run upon the mesentery to form a stem, having a 
curved course, from which other vessels arise to run to the respira- 
tory organ and so may be named pulmonary arteries. With these 
pulmonary arteries the pulmonary veins are in connexion, from 
whose union a longitudinal stem arises from which branches proceed 
to the arterial vessel with which we began our description !. 
Besides the blood-vessels already described there are other 
vessels which in Echinoderms provided with suckers or feet are in 
connexion with these organs of motion. The integument of the 
body is perforated by numerous pores arranged regularly m rows ; 
in the sea-urchins the rows have been called, on account of their 
regularity, Ambulacra, from a comparison with orderly rows of 
trees and garden-walks. Through these pores membraneous cylin- 
drical feelers (the feet) pass out, each terminating in a minute 
suctorial disc. According to the investigations of VALENTIN these 
feelers are in Echini perforated at their extremity by a fine aperture. 
Within the integument there are vesicles in connexion with them. 
The feelers, hollow within, are filled with a fluid, usually sea- 
water, which the animal can press at will from the vesicles, or, by 
contraction of the former, can cause to flow back. In this way the 
animals move their body, the numerous feet contracting and elon- 
gating, and adhering by means of the suckers. ‘There are vessels 
corresponding to the rows of feet or feelers, from which lateral 
branches proceed to the vesicles of the feelers. The ordinary 
number of these longitudinal vessels of the integument is five; in 
the star-fishes their number corresponds with the number of the 
rays of the body. These lymphatics fall into an annular vessel 
surrounding the mouth. In Aolothuria the appendages of the 
feelers which surround the mouth proceed from this annular vessel : 
and from it there arise also five other vessels that descend along the 
commencement of the intestinal tube, where they terminate in 
another annular vessel from which one or two oblong cecal vesicles 
depend (Ampulla Poliana), that are in like manner filled with 
watery fluid ?. 
The change of the blood from venous to arterial, the proper 
1 See TIEDEMANN, Anat. der Réhren-Holothurie, s. 13—18, Tab. 111. ; comp. also 
Cuvier, Régne Anim., édit. ill., Zoophytes, Pl. 18. 
2 See the figures in TrEDEMANN, Tab. It. fig. 4, 6. 
9—y» 
