340 MOLLUSCS. 



The ovary — a large rounded white organ — lies freely in a 

 peritoneal sac near the apex of the visceral mass. From 

 this sac the eggs pass along a short direct oviduct, which 

 opens into the mantle cavity to the left of the anus. Asso- 

 ciated with the oviduct, and pouring viscid secretion into it, 

 are two large " nidamental glands," of foliated structure. 

 Close beside these are accessory glands, of a reddish or 

 yellowish colour, with a median and two lateral lobes ; 

 while at the very end of the oviduct are two other glands. All 

 seem to contribute to the external equipment of the egg. 



The spermatophores pass from the genital duct of the 

 male to the fourth left arm, which becomes covered with 

 them and quaintly modified. This is usual among cuttle- 

 fish, and in some, such as Argonauta and Tremoctopus, the 

 modified arm with its load of spermatozoa is discharged 

 bodily into the mantle cavity of the female. There its 

 discoverers described it as a parasitic worm " HectocotylusT 

 In Sepia, however, the modified arm is not discharged, but 

 simply thrust into the mantle cavity of the female. The 

 spermatophores burst, and the liberated spermatozoa fertilise 

 the eggs apparently in the mantle cavity. 



The laid eggs are enclosed within separate black capsules 

 containing gelatinous stuff", but the stalks of the capsule are 

 united so that a bunch of " sea-grapes " results. 



Second Type of Cephalopod.\. The Pearly Nautilus 

 {Nautilus pompilius). 



The shells of the pearly Nautilus are common on the 

 shores of warm seas, but the animals are very rare. Natur- 

 alists do not seem to know how to get them, though the 

 natives of Fiji and the New Hebrides, who appreciate their 

 flesh, trap them successfully in lobster-pots baited with 

 crustacean or sea-urchin. The animal creeps or swims 

 gently along the bottom at no great depth, and its appear- 

 ance on the surface, " floating like a tortoise-shell cat," is 

 probably the result of storms. It is called " pearly " because 

 of the innermost layer of the shell. This is exposed after 

 the soft organic stratum and the median layer which bears 

 bands of colour have been worn away, or dissolved in a 

 dolphin's stomach, or artificially treated with acid. 



