406 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Echino dermata. 



So-called Heart of Echinoderms.* — Professor E. Perrier, referring to 

 the recent essays by M. Proulio, who disagrees with his results, and by M. 

 Cuenot, who agrees with what he has taught as to the so-called heart or 

 plastidogenous body of Echinoderms, resumes the history of our knowledge 

 of this organ. He thinks that M. Prouho's results are not so essentially 

 different from his as that author seems to suppose. Ho suggests the term 

 organe plastidoghie for the ovoid gland, as it is an organ which produces 

 anatomical elements ; he cannot believe that it has an excretory canal by 

 means of which it is put into relation with the exterior, and he is inclined 

 to agree with M. Koehler's interpretation of the body as an appendage of 

 the so-called vascular apparatus. 



Organization of Echinoidea.t — M. H. Prouho, referring to some dis- 

 puted points in the anatomy of sea-urchins, describes the water-vascular 

 system ; in Dorocidaris he finds an aquiferous system which communicates 

 with the exterior by means of the madrcporitc, and which is formed of 

 canals invested by a vibratilo endothelium ; there is also a " systemo vascu- 

 laire sanguin," or blood-vascular system, for which the author prefers the 

 name of " systemo visceral vasculo-lacnnaire " ; this is in great part formed 

 not of vessels, but of lacunro hollowed out in the mesentery and its ap- 

 pendages ; the internal marginal vessel is only a vast interstitial lacuna ; at 

 the level of their oesophageal rings these systems are closely applied to one 

 another, but do not communicate ; an exchange of currents between the two 

 is impossible. The only changes that can be effected are such as are of an 

 osmotic nature ; a true diaptedesis probably occurs. The visceral vasculo- 

 lacimar system has no communication of any kind with the exterior. The 

 canal which Professor Perrier calls the excretory canal of the ovoid gland 

 is not a dependence of this system, but is an appendage of the aquiferous 

 apparatus which allows the water that enters by the madreporite to come 

 into contact with the walls of this gland. No exchange can be effected 

 between this canal and the contents of the visceral plexus distributed to 

 the walls of the ovoid organ, for it is opjjoscd by a continuous epithelium. 

 The term excretory canal aj^pears to have led to a misunderstanding, and 

 may therefore be well replaced by " annexed aquiferous duct." The 

 contents of the aquiferous system are moved by the vibration of the 

 endothelium of its vessels ; while those of the vasculo-lacunar system can 

 only move by a vis a tergo due to the repletion of the intestinal ab- 

 sorbents. 



The two systems of canals and lacunfc aid in forming the perivisceral 

 fluid whicli not only circulates actively aroimd the viscera, but is also 

 found in the cavity which is absolutely shut off from the visceral, and 

 which contains tho " lantern of Aristotle." The branchial appendages of 

 the Cidarids are, as is now well known, internal and not external, and float 

 in the general cavity. The author regards them as organs charged with 

 the function of keeping an equilibrium between the liquid of the lantern 

 and the perivisceral fluid whicli is outside it ; this equilibrium is not one of 

 pressure but of osmotic action. 



Movements of Star-fishes.J — Prof. W. Preycr's subsidiary title to this 

 memoir will probably be a little astonishing to those who look on 

 Echinoderms as some of the " lower Invertebrates " — it is " a comparative 

 physiological-psychological investigation." The author was led to under- 



* Coraptes Kendus, civ. (1887) pp. lSO-2. f IWd., pp. 70G-8. 



X MT. Zool. Stilt. Ncapel, vii. (18SG) pp. 27-127 (27 fig:.«.). 



