312 



CHARACTERS OF INVERTEBRATE ANIMALS 



similarly provided. Outside the circlet of arms a large eye can 

 be seen on either side, covered by a circular eyelid perforated 

 by a small hole. The presence of mouth and eyes shows that 

 we are dealing with the head end of the animal. In comparing 

 the body with that of the Ormer we must place this end down- 

 wards and slant the rest of the animal, which is mostly visceral 



MANTLE CAVITY 



jnSCERAL HUMP 



VENTRAL 

 GANGLIA 

 ■MOUTH CAVITY 

 RADULA 



Fig. 179. — The Cuttle-Fish {Sepia officinalis) reduced 

 A, View from left side. A, Side-dissection. Arrows show course of water into and out of mantle cavity. 



hump, upwards and backwards as shown in the diagram (a). It 

 will then be clear that the long axis of the body is pretty nearly 

 at right angles to the direction corresponding to the long axis 

 in the Ormer. The long visceral hump will possess two gently- 

 curved sides facing respectively forwards and backwards, and 

 two sharp edges placed right and left and margined by a fin-like 

 expansion. The next point will be to find mantle and foot. The 

 former is readily made out running round the edge of the large 

 visceral hump at its lower end, just above a narrowed " neck " 

 indicating the boundary of the head. Most of it is at the back, 

 where it constitutes the hinder wall of a large mantle-cavity, 

 into which a large slit-like opening leads. The foot has grown 



