I40 IIERMAniRODITE MOLLUSCA, GENERATIVE ORGANS chap. 



In Octopus vvlgaris, the species referred to by Aristotle, the 

 hectocotylised arm is short, tliin in its outer half and pointed at 

 the extremity, while tlie fold of skin is very white, and gives 

 the arm an appearance of being divided 1)y a cleft at the side. 

 At the same time, an nnnsual development of one or two suckers 

 on the arm is not uncommon.^ 



Fig. 52. — Octoims lentus Baird, N. Atlantic, showing the peculiar formation of the 

 heutocotylu.s arm, h.a. (After Verrill, x ^.) 



It is believed that in the Tetraljrancliiate Cephalopoda. 

 {Nautilus) a union of the four inner ventral arms may correspond 

 functionally to the hectocotylising of the arm in the Dibranchiates. 



Hermaphrodite MoUusca. — («) Monogoywpora. — The repro- 

 ductive system in tlie hermaphrodite Mollusca is far more compli- 

 cated than in the dioecious, from the union of the male and female 

 organs in the same individual. As a type of the Monogonopora, 

 in wliich a single orifice serves for both male and female organs, 

 may be taken the connnon garden snail {Helix aspersa), the 

 accompanying figure of which is ch^awn from two specimens 

 found in the act of union (Fig. 53). 



Beginning from tlie inside and proceeding outwards we have 

 firstly the hei-mapliroditc gland or ovo-testis (h.G.), a yellowish 

 white mass of irregular shape, embedded in the liver (l.) and 

 forming part of its spiral but not reaching quite to the apex. 

 Within this gland are developed the ova and spermatozoa. The 

 former are rather large round cells, produced within the outer 

 wall of the gland, while the spermatozoa, which are produced in 

 the more central part, are threadlike bodies, generally aggre- 

 gated in small bundles. From the hermaphrodite gland the ova 

 1 Steenstrup, Ann. Mag. Nat. Hid. (2), xx. p. 81 f. 



