144 s - STILLMAN BERRY. 



noticed as being luminous at that period, but now we know that 

 the firefly and glow-worm pale in comparison, and that probably 

 not even the brilliant display of the tropical elaters can vie with 

 the gorgeous pyrotechnics of certain squids. It is indeed quite 

 possible that the latter exhibit the highest development of the 

 photogenic function known in the entire animal kingdom. 



2. CLASSIFICATION OF CEPHALOPODS. 



Living members of the Molluscan Class Cephalopoda cleave 

 simply and naturally into two well-defined, easily separable 

 groups. The first of these, and that universally regarded as 

 the most primitive, is the Order Tetrabranchiata, comprising 

 only the few species contained in the single genus Nautilus. 

 The animals of this group are characterized especially by the 

 possession of a massive, chambered, external shell; of a "funnel" 

 formed by the appression of two lateral folds which remain 

 unfused in the median line below; of a system of suckerless 

 lobes around the mouth, bearing retractile, annulated tentacles; 

 of such traces of metamerism as the presence of two pairs each 

 of ctenidia, "branchial hearts," auricles, renal organs, and 

 osphradia; and of a simple "pin-hole" eye, open to the exterior. 

 Ink-sac and chromatophores are absent. 



The second group, Order Dibranchiata, comprising all living 

 cephalopods except Nautilus, is characterized by either the 

 complete atrophy of the shell or its reduction in the adult to a 

 concealed loose coil (Spirulidae), a calcareous plate (Sepiidse), or 

 a horny pen; by an entire, tubular funnel; by the development of 

 the anterior portion of the primitive foot into a series of eight or 

 ten muscular, sucker-bearing, tentacle-like arms about the 

 mouth; by but a single pair each of ctenidia, branchial hearts, 

 auricles and renal organs; by the presence, at least typically, of 

 highly developed eyes; by the development of complex, special- 

 ized pigment cells in the skin; and by the presence of the peculiar 

 "ink-sac." Osphradia are absent. 



The Dibranchiata in their turn are sharply divisible into 

 two subgroups, the Decapoda and Octopoda. The former are 

 mainly pelagic; have finned, generally elongate bodies; have not 

 only the eight "primary" arms of the octopods, but a pair of 



