50 American Seashells 



female also differs in having its two dorsal arms enlarged at the end to form 

 a veil or mold with which she secretes a shell. In a vast number of species, 

 the males are characterized by having one of the arms modified to form a 

 copulatory organ. This arm is known as the hectocotylus. In certain octo- 

 pods, including the Argonauta, this arm is broken off and left in the female 

 to fertilize the eggs. In all the other groups the hectocotylus is simply held 

 inside the female until copulation is complete. It is interesting to note that 

 more than 2000 years ago Aristotle recorded the presence of the hecto- 

 cotylus arm in the octopus and correctly associated it with its sexual purpose. 



In the males the sperm is gathered into large sacs or spermatophores 

 of several inches in length. These sacs find their way in some unknown 

 manner into the hectocotylus arm. Each sac contains a tiny, coiled, spring- 

 like filament which spews the ripe sperm out of the sac. 



The eggs of the cephalopods are laid in various ways. They may be 

 single and floating in the pelagic species, such as Oegopsida, congregated 

 together in a shelly nest as in Argonmita, laid in jelly tubes as in the Loligo 

 squid, or anchored in grape-like bunches under rock ledges as in the Octo- 

 pus. The embryo emerges from the tgg fully developed and does not have 

 a free veliger stage. With the aid of a lens it is possible to see the beautiful 

 splotches of bright chromatophores in the skin of the tiny young even before 

 they hatch. About a hundred eggs are laid at one sitting by the octopus; 

 the squid tgg strings from one female may contain over 40,000 eggs. Some 

 species of octopuses take pains to watch over their brood of eggs and from 

 time to time may carefully go over them with their tentacles to remove dirt. 



THE CHn01<iS—AMPHINEURA 



Amateurs and professionals alike have found the chitons or coat-of-mail 

 shells an extremely interesting and fruitful field of study, and no collection 

 is complete without at least three or four representatives of this strange 

 group of mollusks. The chitons closely resemble the gastropods except that 

 they bear eight shelly plates. For those who wish to excel in a more serious 

 study of a relatively small class of mollusks, no more inviting series of species 

 awaits the collector than our chitons of the rocky shores. They are dealt 

 with in this book in some detail, for no popular shell book has hitherto at- 

 tempted to open the doors to this supposedly "difficult and poorly known" 

 group. 



There are nearly fifty species in our Atlantic waters and perhaps twice 

 that number on the Pacific Coast, and yet this represents fewer species 

 than are found in the single family of Wentletraps or Epitonium. Some 

 private collectors, such as the late Dr. R. B. Bales, were able in a few years 

 to make larg^er and finer collections of Florida chitons than are found even 



