132 MOLLUSCA. 



portion. These are connected by connectives with the supra- 

 esophageal ganglia. .- 



5. The infra-buccal ganglia, about the same size as, and lying 

 ventral to, the supra-buccal ganglia, and connected with them 

 by connectives that run around the esophagus. 



Draw a figure of a sagittal section of the head. 



Two large ganglia, the optic ganglia, lie against the eyes 

 and will be seen in cross-sections of the head that will be studied 

 later. A dissection of one side of the head will show one. 



Open the animal along the mid-dorsal line and find the pen 

 which is embedded in the mantle. After exposing it for its 

 full length, turn the flaps aside and see that it lies in a pocket. 

 It probably represents a modified shell that has become entirely 

 inclosed by the mantle. What is its function? 



Pull the pen out of the mantle and draw it. 



With a razor make cross-sections of a squid, a quarter of an 

 inch thick, and arrange them in order, in a little water, as they 

 are made. Identify the parts you have found in dissection. 



Make drawings of the sections that pass through the infra-eso- 

 phageal ganglion, through the eyes, through the liver, and through 

 the heart. 



If time permits, study prepared sections that have pre- 

 viously been made. The structure of the eye and the positions 

 of the parts of the nervous system should receive special atten- 

 tion. 



Specimens of other cephalopods, such as Octopus and Nau- 

 tilus, should be compared with the squid and the adaptations 

 that fit them for their particular lives noted. 



Brooks: The Development of the Squid (Loligo Pealii). Mem. Bost. 

 Soc. Nat. Hist., 1880. 



: Handbook of Invertebrate Zoology. 



Drew: Sexual Activities of the Squid. I. Copulation, Egg-laying and Fer- 

 tilization. Jour. Morph., 22, 1911. 



Griffin : The Anatomy of Nautilus pompilius. Mem. Nat. Acad. Sci., 8, 1900. 



Vialleton: Recherches sur les primieres phases du deVeloppment de la Seiche 

 (Sepia officinalis). Ann. Sci. Nat. (7) Zool., 6, 1888. 



Willey: Contribution to the Natural History of the Pearly Nautilus. 

 Willey's Zool. Results. 4, Cambridge Univ. Press, 1902. 



Williams: The Anatomy of the Common Squid, Loligo pealii. Amer. 

 Mus. Nat. Hist. 



