Dr. D. Bergendal ow the Land- Planar icb. 45 



jaalia an external sexual orifice can be easily detected even in 

 small individuals ; but in this case I have never succeeded in 

 doing so even in larger animals. About 1 centim. behind the 

 mouth one sometimes sees a slight impression, which perhaps 

 might be regarded as an indication of this aperture. 



The creeping movement of the worms is effected almost 

 exclusively by the long and strong cilia which clothe the sides 

 of the creeping-sole. The middle of the margin of this is set 

 with short strong cilia, which, however, move very feebly. 

 When creeping t'he worms are almost cylindrical ; in fact the 

 dorso-ventral axis is even longer than the transverse axis. 



Multiplication hy Transverse Division. 



The number of sexually immature animals has greatly 

 increased in the conservatory. Even in the autumn a great 

 number of small worms were to be observed. Close exam- 

 ination showed that many of these presented no heads, and 

 that in others the development of the heads was very unequal. 

 Animals which were cut with a pair of scissors into several 

 pieces did not die, but each piece formed a new head and 

 mouth. In the renewal of the head a white point is first of 

 all developed, and this gradually enlarges. At first the 

 streaks of the body can usually be traced on to the young 

 head-lobe. With the development of the papillas and eyes 

 the typical pigmentation also makes its appearance. The 

 renewal of the pharynx can be noted from without during its 

 progress by the fact that the middle dorsal streak becomes 

 widened over the spot where the mouth is being formed. 



I have also observed spontaneous transverse division. 

 Three times animals from which I had cut away cephalic 

 portions of considerable size constricted off corresponding 

 pieces from the posterior extremity, and all the three pieces 

 afterwards became regenerated. Once, under such circum- 

 stances, two posterior pieces were thrown off. On separating 

 a smaller anterior portion I have observed no posterior ab- 

 striction ; nor does such a thing always occur when larger 

 pieces are cut off. It would seem that this depended upon 

 whether the animals had been previously well nourished. 

 These worms also divide without having received any external 

 injury. 



These Bipalia are generally found in the reversed pots 

 upon which the pots with plants stand ; and I once found in 

 such a pot three pieces which had been produced from one 

 worm by transverse division. The plants had not been 

 moved for a fortnight or three weeks, and the fissional cica- 



