356 Miscellaneous. 



contracts at its upper part to lodge the ambiilacral ring, and sends 

 a flattened prolongation to the dorsal surface of the arms (dorsal 

 space). Within the aquiferous ring we find the nervous band form- 

 ing a complete ring around the oesophagus. To find this we have 

 to tear a membrane which envelops it and separates it from the 

 general cavity ; then we see the injection which fills the space situ- 

 ated beneath it and surrounds the nervous system (perinervous 

 space). If, now, we make a section of an arm, we find in the lower 

 part a furrow hollowed out in the discoidal ossicle, and which con- 

 tains the ambulacral canal and the brachial nerve. This latter, 

 flattened and bent into a crescent-like form, is in contact with the 

 canal by its thin margins, and thus bounds a rounded space inde- 

 pendent of the cavity which surrounds it (radial space). What are 

 the relations of the perinervous space and of the radial space to the 

 general cavity ? Around each ambulacral canal going to an arm 

 there is a space hollowed out in the calcareous pieces and connected 

 with the general cavity ; in the same way, ai'oimd every nerve issu- 

 ing from the ring there is a space communicating with tho envelope 

 of the band. Now these two spaces advance to meet each other, at 

 the same time as the parts which they contain, and unite at the 

 level of the furrow, thus placing the perinervous space widely in 

 communication with the general cavity. The two spaces unite into 

 one, which occupies the whole cavity of the furrow enveloping the 

 vessel and the nerve (peripheral' space), and occupying the circular 

 interspace between these two organs (radial space). Lastly the 

 general cavity communicates with the incrusted envelope already 

 indicated as surrounding the sand-canal and the heart, which was 

 long regarded as the sand-canal itself (stone-cancd of authors). 



These observations show that no system of proper canals exists, 

 but spaces in close connexion with the general cavity. 



On observing a living animal from the dorsal side we see its body 

 swell up and collapse alternately ; if we turn it over in a liquid con- 

 taining coloured particles we see a double current around the genital 

 slits. By injecting a coagulable liquid through one of these slits 

 we find that the onfice gives access to a large, closed sac, dilated 

 in its ventral region, contracted towards the back, immersed in the 

 general cavity, and having on its outer surface the genital utricles. 

 These sacs, first seen by Ludwig, who suspected their function, 

 were nevertheless regarded by him as appendages of the generative 

 organs, and received the name of pouches. Experiment, and espe- 

 cially the close relations of the sac with the nutritive liquid of the 

 general cavity, must lead us to consider them true respiyxitorn sacs. 

 From these facts we regard the circulatory system as formed by the 

 general cavity and the sjjaces connected with it ; and we think that 

 the respiratory sacs, by their alternate collapse and dilatation, invite 

 the blood into the peristomachal cavity and afterwards drive it to 

 the periphery. This very simple arrangement explains how the 

 blood, bathing all the organs, respires and is set in motion. — 

 Comptes Rendus, February 21, 1881, p. 421. 



