7O Invertebrate Zoology. 



A CEPHALOPODOUS MOLLUSK 



(Loligo pealii). 



External Anatomy. Note the elongated body, sepa- 

 rated from the movable head by a constricted neck. The 

 integument is abundantly supplied with chromatophores. 

 Though not of the usual morphological significance, observe 

 that there is an anterior and a posterior end, and a dorsal 

 and a ventral surface. What is the shape and attachment 

 of the terminal fins ? Demonstrate that there is an opening 

 between the neck and the " collar " into a central chamber, 

 the mantle cavity. What is the position of the eyes ? Are 

 they provided with lids ? How many arm s are there ? Are 

 all of the arms of the same structure ? How many rows of 

 suckers are there on the shorter arms? On the longer? 

 Do you find the mouth ? The opening of the siphon-tube ? 

 Just back of each eye, note the fold of the olfactory organ. 

 What is its extent? Note the median, dorsal projection of 

 the collar. Turn it back, and note that it is stiffened by the 

 presence of a horny structure. 



Open the animal along the mid-dorsal line. The horny 

 structure, pen, will be found to extend the entire length. 

 Remove the pen. 



Make a drawing of the animal as seen from the left side, 

 putting in as much detail as possible and naming the parts. 

 Also make a drawing of the pen. 



