Miscellaneous. 197 



direction of these prolongations is variable. At the level of the 

 median furrow presented by each of the ambulacral cords it is 

 exactly transverse. We can then trace these prolongations even 

 into the branches destined for the ambulacral tentacles. I may add 

 that these cells are formed of a not very abundant homogeneous grey 

 protoplasm surrounding a large clear nucleus. The cellular layer 

 adheres intimately to the fibrous layer, so that they can only be 

 separated from each other in the state of little fragments. 



2. Muscles. — The most contradictory statements prevail with 

 regard to the structure of the muscles of the sea-urchins. I have 

 been able to ascertain that they are composed of very thin cylindri- 

 cal fibres, perfectly smooth and homogeneous in the direction of 

 their length. Thus, even by employing alcohol, osmic acid, haema- 

 toxyliu, chromic acid, &c., I have not been able to discern the least 

 trace of a transverse stria. These fibres present a fibrillar structure, 

 and frequently one or more elongated nuclei applied to their surface ; 

 but they appear to be destitute of an enveloping membrane. They 

 are birefringent and become vividly impregnated with colouring 

 matters and osmic acid. 



The fibres of the muscles of the lantern of Aristotle are implanted 

 directly by a denticulated extremity upon the calcareous parts of the 

 skeleton. 



The muscles of the lantern and the muscular organs (intestine, 

 ambulacral vesicles) undergo energetic contractions under the in- 

 fluence of electrical or mechanical excitation; but these contractions 

 do not take place suddenly as in the case of striated muscles. It is 

 very difficult to demonstrate the existence of the nerves which 

 animate these muscles. — Comptes Mendus, Nov. 6, 1876, p. 860. 



Physiological Experiments on the Functions of the Nervous System 

 in the Echinida. By M. L. Fbedericq. 



By means of fine-pointed scissors five small cuts were made in 

 the buccal membrane of an Echinus lividus, in such a manner as to 

 divide the ambulacral nervous trunks near their origin in the collar. 

 The ambulacral feet were not at all paralyzed ; they moved in all 

 directions and attached themselves to surrounding bodies ; but the 

 animal could no longer execute general movements or change its 

 position, whilst other iminjured individuals could walk along the 

 bottom of the aquarium and crawl up its glass front. 



If an uninjured Echinus be turned so that its mouth is upwards, 

 it moves its ambulacral feet until, in a few seconds or minutes, it 

 will assume its normal position. After section of the ambulacral 

 nerves the animal could no longer execute this combined movement, 

 but remained indefinitely in its abnormal position. This is the 

 effect of an insignificant mutilation. On the other hand the most 

 serious lesions, if they do not reach the central nervous system, by 

 no means prevent the urchins from using their ambulacral feet in 

 the ordinary way ; they turn themselves perfectly after many inci- 



