parts, instead of being enclosed in a shell, reverse 

 the order and themselves enclose the shell. 

 Throughout the cephalopods, this shell shows vari- 

 ous stages of degeneration; completely disappear- 

 ing in the octopus, a close relation of the squid. 



Properly speaking, the squid swims neither 

 "backward" nor "forward." The so-called tail fin 

 is not at the posterior end of the body, but is at 

 the highest point of what is actually the back. And 

 strange as it may seem, the sucker-bearing "arms" 

 of this paradoxical creature are in reality its foot. 

 How the sucker-arms were derived from the fore- 

 part, and the siphon from the middle part of the 

 foot, while the cone-like body had become elon- 

 gated in a dorsal direction — in truth, the way in 

 which all its evolutionary changes have been 

 brought about would make an interesting tale in 

 itself, had we the time to take it up. 



My employment of the term "hectocotylized 

 arm" in the opening section of this monograph 

 must have puzzled the lay reader — even as I was 

 puzzled when first I came upon it in the literature 

 of the cephalopods. Perhaps, also, the reader — as 

 I, too — looked up its meaning in modern diction- 

 aries or reference works, and with the same result; 



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