I40 HERMAPHRODITE MOLLUSCA, GENERATIVE ORGANS chap. 



at the extreme tip with a peculiar kind of plate, which connects 

 with the membrane at the base of the arm by a channel of skin, 

 which probably conveys the spermatophores up to the tip> 



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

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

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

 the arm an appearance of being divided by a cleft at the side. 

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

 on the arm is not uncommon.^ 



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

 hectocotylus arm, h.a. (After Verrill, x i.) 



It is believed that in the Tetrabranchiate Cephalopoda (^JSTauti- 

 lus) a union of the four inner ventral arms may correspond func- 

 tionally to the hectocotylising of the arm in the Dibranchiates. 



Hermaphrodite Mollusca. — Qct) Monogonojjora. — The re- 

 productive system in the hermaphrodite Mollusca is far more 

 complicated than in the dioecious, from the union of the male 

 and female organs in the same individual. As a type of the 

 Monogonopora, in which a single orifice serves for both male 

 and female organs, may be taken the common garden snail 

 (^Helix aspersa')^ the accompanying figure of which is drawn 

 from two specimens found in the act of union (Fig. 53). 



Beginning from the inside and proceeding outwards we have 

 firstly the hermaphrodite 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 

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



