76 



ZOOLOGY 



on the other hand two curious organisms, the CoeloplaTia of 

 Kowalevsky and the Ctenoplana of Korotneff, have lately been 

 discovered which unite some characters of the Ctenophora 

 with others of the Turbellaria. 



In a typical Ctenophor, one of the Cydippidae, such as 

 ITormiphora, the mouth leads into a flattened stomach hned 

 with ectoderm, which in its turn opens iato the funnel, Uned 

 with endoderm (Fig. 53). The funnel gives off two gastric canals, 

 which pass out towards the base of the long tentacles. These 

 two primary canals give off a secondary canal on each side, 

 which forks, and forms tertiary canals (Fig. 54), of which there- 

 fore there are eight. Each of these eight canals opens into 

 one of eight meridional canals which lie under the rows of 

 vibratile plates, and which end blindly both at the oral and 

 aboral pole. 



The two long tentacles can be completely retracted into their 

 pouches ; they bear peculiar adhesive cells. 



The characteristic vibratile plates are formed by a number 

 of very large cUia fused together side by side ; an arrangement 

 also met with in some of the Hypotricha. 



The central nervous system consists of an area of ciliated 



Fig. 54. — Hormiphora plumosa. 

 After Chun. Aboral view. 



2. Aboral pole with sense organ. 



5. One of tlie eight bands of 



fused cilia. 



6. One of the eight canals running 



towards 5. 



8. A tentacle. 



9. Gelatinous tissue. 



SS. sagittal plane. 



cells at the aboral pole. This area is sunk into a depression 

 which contains certain otoliths, and from which nerve cells 

 pass to the meridional rows of paddles. This specialised sensory 



