440 



MOLLUSCA. 



The nidamental glands are accessory glands of the female, which secrete the 

 egg envelopes and open into the mantle-cavity. In Nautilus there is a single 

 gland in the mantle-wall dorsally. In Decapoda they are in the anterior wall 

 of the mantle-cavity superficial to the kidneys, and there are generally two pairs 

 the ventral being the smaller (Fig. 354, Ad, Nd). 



The eggs are surrounded (Argonauta, Octopus, Sepia) by capsules 

 with long stalks, which are united together in racemose masses (so- 

 called sea-grapes), and fastened to foreign objects in the sea. In 

 other cases the eggs are aggregate^ in gelatinous tubes which may be 

 attached together in great numbers (Loligo). In Argonauta they are 

 placed in the shell. 



The spermatopliores (Fig. 353) are manufactured in the male 

 generative ducts. They are elongated, vermiform bodies containing 

 spermatozoa, and often presenting a most elaborate structure. In 

 Dibranchs they may be described as tubes containing spermatozoa 

 at one end, and a piston and spiral elastic spring at the other. 

 We may presume that under proper conditions the spiral spring 

 elongates and drives down the piston, which then expels the 

 spermatozoa. 



The spermatophore are sometimes very long : in Eledone 8 centi- 

 metres, in Octopoda with autotomous hectocotylus they may attain 

 a length of 50 centimetres; and in Nautilus, in which they are coiled 

 on themselves, they may be more than 30 centimetres long. 



In the Dibranchs one of the 

 arms of the male is always modi- 

 fied, or hedocotylized as it is called, 

 for purposes of copulation. In 

 the Decapoda it is usually the 

 fourth left arm ; but in Enoplo- 

 teuthis it is the fourth right, 

 and it may vary from the fourth 

 right to the fourth left in the same 

 species ; in Idiosepius and Spirula 

 both right and left fourth arms 

 are modified, and in Spirula en- 

 closed in a common envelope ; in 

 Octopoda it is usually the third 

 right, but in Scaeurgus and Argo- 

 nauta it is the third left, and the 

 second right in Cirroteuthis. In 

 most cases the modification con- 

 sists mainly in a reduction of the 

 suckers, and the arm is not de- 

 tached ; it affects the extremity of 

 the arm in Enoploteuthis, Eledone, 



FIG. 355. Male of Argonauta argo (after H. 

 Miiller). He hectocotylized arm. 



