92 



ZOOLOGY 



The family Microstomida is unique in the group in possess- 

 ing the property of asexual reproduction, which takes place by 

 transverse fission. The posterior third of the 

 body becomes cut off by a septum, and grows 

 until it equals in size the anterior half. 

 Then each portion again cuts off its posterior 

 third, and these again grow (Fig. 64). By 

 this process of segmentation and equalisa- 

 tion chains of 4, then 8, then 16, and some- 

 times even 32 individuals are formed. Each 

 forms a mouth, and for some time the chain 

 persists, but the individuals ultimately 

 become sexually mature and then separate. 

 They lay eggs during the autumn, which 

 persist through the winter, and these give 

 rise in the spring to the budding individuals. 

 Two curious animals, the Coeloplana and 

 the Ctenoplaiia, have recently been described 

 by Kowalevsky and Korotneff respectively, 

 which are intermediate in structure between 

 the Ctenophoka and the Tuebellaeia. 

 Coeloplana is minute, its flattened body 

 covered with cilia, creeps along the surface 

 on its ventral face. In the middle of its 

 back is a sensory vesicle enclosing an otolith. 

 Fig. 6i.— Microstoma On each side of its body, at right angles to 

 Slivido;. "ht; the plane of the stomach, is a long feathered 

 are 16 individuals, 8 tentacle which Can be withdrawn into a 

 rhSIWd^f pouch. The mouth in the middle of the 

 the first (m), second ventral surface opens into a stomach which 



(m'), 'third (to"), and . ™ , . , , 



fourth (m'") genera- gives off numerous anastomosmg canals, two 



tion. The iifth gen- ^f y^hich pass dorsally, one in front and one 



acquired a mouth behind the otocyst, and there end blindly, 

 aperture. After Von Cteuoplana has much the same shape as 



r Ciliated grooves. Ooeloplana. In addition to the uniform 



2. Eye spots. covering of cilia, there are on the dorsal sur- 



3. n es ine. ^^^^ eight bands of ctenophoral plates corre- 

 sponding to those of the Ctenophors. The alimentary canal 

 resembles that of Coeloplana. The sense organ, situated in the 



