66 COMPARATIVE PHYSIOLOGY OF THE BRAIN 



surfaces is a pronounced reaction of Echinoderms and 

 is quite common in other animals, for instance in the 

 Actinia mesembryanthemum of the Mediterranean, 

 and in the Coccinelli. This tendency is also present 

 in plant-organisms -- for example, Plasmodia,-- and 

 here Sachs has traced it back to negative geotrop- 

 ism. I will repeat here the description which I have 

 already given in a former publication of the phenome- 

 non as it appears among Echinoderms (3). 



No one who observes the animals on rocks or posts 

 near the surface of the ocean when the water is quiet 

 can fail to notice the relatively large number of 

 Echinoderms. Many of these for example, the Cu- 

 cumaria cucumis, which is very common in the Bay 

 of Naples always live near the surface, not beyond a 

 depth of about 30 m. It can be shown that Cucuma- 

 ria, like Plasmodia or Coccinelli, are forced, when on 

 vertical surfaces, to crawl upward. Cucumaria has a 

 slender pentagonal body, 10 cm. or more in length, 

 with radial, branchino- tentacles on its oral end. 



o 



There are five ridges on the body, and in these are 

 situated longitudinal rows of tube-feet, by means of 

 which the animal crawls upward, even on smooth 

 glass walls. If placed in an aquarium, it crawls about 

 on the bottom until it comes to a vertical side ; it then 

 crawls upward and remains on the highest point, if 

 possible just below the surface of the water. This 

 position then usually becomes permanent, and the 

 animal is converted into a sessile organism. 



If a Cucumaria is allowed to attach itself to a 



