GLAND OF BOJANUS. 507 



bivalve upon its back (that is to say, upon that part of its circumference 

 which corresponds with the hinge), the student will observe on each side 

 of the visceral mass an oblong body of variable tint, the shape of which 

 depends more or less upon that of the animal. 



(1333.) The structure of this gland is rather complicated, its interior 

 being made up of numerous cavities communicating with each other. 

 Its relations with the generative system present themselves under three 

 aspects : sometimes the reproductive glands open immediately into its 



Fig. 254. 



Gland of Bojanua. 



cavity ; sometimes the two open externally by a common orifice ; and 

 sometimes two distinct orifices, more or less separated from each other, 

 belong to each of the glands. The circulation through this remarkable 

 viscus is of a venous character, and represents a portal system : hence it 

 has been alternately regarded as a respiratory organ, a testicle, and a 

 urinary apparatus ; its real office, however, is still problematical. 



(1334.) On throwing injection into the genital orifices*, the sexual 

 glands become tinged, and on examining fragments of such genital 

 glands microscopically, the injected substance may be seen mixed with 

 the ova and spermatozoa. These facts may be observed with special 

 ease in the common Cockle (Oardium edule), 



(1335.) Sometimes the ova may be seen actually laid by living fe- 

 males of Modiolce and Mytili, one of the valves of whose shell has been 

 removed, on irritation of the genital orifice ; and in others, the ova or the 

 spermatic fluid may be made to pass out of their orifices at the breeding 

 season by pressing gently upon the foot. In Spondylus gaderopus, 

 the genital orifice is situated in the sac of Bojanus, where the eggs may 

 occasionally be seen issuing forth, in aspect like a thread of vermicelli, 

 composed of reddish ova mixed with mucus. 



* Fide memoir by Dr. H. Lacaze-Duthiers, Ann. des Sci. Nat. 4 e s6r, t. ii. 



