900 SUMMARY OF CURRENT RESEARCHES RELATING TO 



movement of the vibratile cilia, which would oppose the formation of 

 gas bubbles, and in the absence of any internal cavity in which the gas 

 cou'.d accumulate or circulate ? 



"in reality, no vegetable or animal which is completely aquatic 

 ever gives off gas under normal and regular conditions, and Convoluta 

 offers no exception to this rule. In the presence of an excess of car- 

 bonic acid aquatic plants only give off oxygen when they present air 

 passages where the leaves are detached from the stem, or when there 

 is a layer of air on their surface." When there is an abnormal 

 quantity of carbonic acid Convoluta deposits in its mesoderm very 

 small grains of amyloid matter ; it is killed when the excess of carbonic 

 acid is too great. C. schultzii, then, absorbs through its cuticle 

 carbonic acid in dissolution, which the chlorophyll decomposes in 

 producing oxygen. This is wholly or partly utilized by the animal, 

 in such a way that, if oxygen is expired, it can only be in very small 

 quantities, and, under normal conditions, not in the gaseous state ; the 

 mode of respiration has a striking analogy to that of submerged 

 aquatic plants. 



Echinodermata. 



Structure of Echinoderms.*— C. F. Jickeli has a preliminary note , 

 in which he states that he has made experiments confirmatory of the 

 doctrine of Carpenter as to the nervous system of Comatula. He 

 finds that a single arm gives no response when the ambulacral groove 

 is touched with a needle or stimulated by an electric current, but that 

 the moment the needle touches the point at which the axial cord lies 

 the arm is strongly flexed, and the pinnules move actively. A 

 single cirrus when stimulated appears to be thrown into a tetanic 

 condition. Many of the author's experiments are in exact agreement 

 with those of Carpenter. After the removal of the visceral mass 

 irritation of the capsule produces a synchronous contraction of all 

 the arms. If a few drops of osmic or acetic acid are put in the water 

 the " torso " moves as actively as an uninjured animal. 



The author describes the structure of the cirri, and the processes 

 which pass from the " spongy organ " into them. The observations of 

 P. H. Carpenter that nerve-branches pass into the dorsal and the 

 ventral muscles is confirmed. A series of sections shows that the 

 ambulacral nerve diminishes in extent as it approaches the intestine, 

 and finally disappears. Attention is drawn to the fact that Gotte 

 describes the epithelium of the so-called ambulacral groove of Comatula 

 as being endodermal in origin. 



A third nerve-centre is described as being present in the con- 

 nective tissue, and as forming a pentagonal cord around the mouth. 

 The lateral cords are connected by branches with one another at the 

 angles of the pentagon, and they extend along the water-vascular 

 system. Each of these cords gives off lateral branches at regular 

 distances, and these innervate the water-vascular system and the 

 papillse of the tentacles. Other well-developed branches are also 



* Zool. Auziig., vii. (1884) pp. 3i6-9, 36G-70. 



