LOLIGO PEALII. 9 1 



may be partly retracted by means of muscles to be shown later. 

 The outer covering of the squid is, therefore, not the true body 

 wall but the mantle. Refer here to your notes on the mussel 

 and the snail, a study of which forms should have preceded this. 

 The free edge of the mantle, surrounding the neck, is called the 

 collar. 



i) Protruding from the collar on one side of the body is a funnel- 

 shaped organ, the siphon. Note its terminal opening. The 

 siphon may also be partly retracted into the mantle cavity. 



Exercise i. Make a drawing of the side of the animal on which the siphon 

 is located, reducing the scale to one-half natural size. 



Exercise 2. Draw a top mew of one of the suckers, and a side view of the 

 same after it has been split vertically through the cup and the peduncle. 

 Enlarge enough to show detail. 



ORIENTATION OF THE SQUID. In order to avoid confusion no 

 reference has thus far been made to anterior and posterior end or to dorsal 

 and ventral surface of the animal. To get a clear idea of these relations 

 of parts stand the squid on its head, spreading out the arms so that it will 

 maintain this erect position. The arms now correspond in position, 

 and are really homologous in development, to the hatchet-shaped foot 

 of the mussel and the broad, creeping belly-foot of the snail; hence the 

 term Cephalopod (head-footed). The siphon is also a modification of 

 a part of the foot that part which, from the position of organs in the 

 mantle cavity, is shown to be the posterior. The surface on which the 

 siphon is located is thus in reality the posterior and that to which the fin 

 is attached the anterior. The ventral surface is represented by the end 

 of the head and the outspread arms on which the animal is resting, while 

 the dorsal surface is reduced to the rounded opposite end of the body. 



Since the squid never naturally maintains this position, however, but 

 rests or swims about with the longer axis of the body in a horizontal 

 position, we shall hereafter in these notes disregard the true morpho- 

 logical relation of parts and call the head the anterior end for convenience 

 sake. From this it will follow that the rounded tapering end of the 

 body will be the posterior. The surface having the fin is uppermost in 

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