Japanese Tricladida Mari cola. j[.Q 



sion that such a reduction uf the rhabdite.s is a special adaptation; 

 I shall now quote his own words. He says, " I)ie Rückbildung 

 der Rhabditen korrespondiert mit meiner Annahme, dass die 

 Rhabditen Schutzorgane sind, die auf Druck aus dem Epithel 

 heraustreten. Offenbar sind sie l)ci den Bdellouriden, die ge- 

 schützt auf der konkaven Bauchtliiche und zwischen den Kiemen- 

 blättern des Limulus leben, infolge Funktionslösigkeit zurück- 

 gebildet worden." However, the fact that the epidermis is in 

 Ectoplana and 3Iicropharynx always full of minute rhabdites lends 

 probabilit}^, in my opinion, to the view that his hypothesis cannot 

 be regarded as a perfect truth. Of course, I believe that the 

 rhabdites are of use to the animal for protection. 



Locomotion. — Like the other planarians, the freely living or 

 parasitic worm is very active in its movements, creeping with 

 steady, rapid motion over smooth surfaces, crawling after the 

 manner of geometer caterpillars, or swimming on the surface of 

 the water. 



Gliding is the most usual mode of progressive movement 

 when the worm is not disturbed, and so far as I have been able to^ 

 observe, it is a combined reaction, brought about partly by mus- 

 cular rhythmic, wav}^ motion of the ventral body- wall and partly 

 by the action of the cilia in the mucus layer between the ventral 

 surface of the body and the surface of which they are moving, the 

 thin layer of mucus being secreted constantly. 



Crawling is induced only when the animal is stimulated in. 

 certain ways, and of course, takes place by a successive alternation 

 of the active muscular contraction and stretching. The ventral 

 surfaces of the anterior and posterior regions of the body act like 

 suckers as the worm loops. While the anterior end holds, the 

 posterior is freed and then drawn up. Such looping fashion was 

 particularly well observed in Ect. limuli. 



Although certain species of Rhabdocoele can freely move by 

 the ciliary reaction through the water, such a swimming is never 

 seen in the Triclads. However, our forms, with their ventral 

 surface uppermost, are able to creep along the water surface. This 

 sort of movement seems to be brousrht about bv the action of the 



