1S4 
ANOltONTA — REPRODUCTIVE SYSTEM. 
visceral mass, above tbe muscular part of the foot and investing the 
convolutions of the intestinal tract : they are however of the simplest 
ami most primitive character ami very similar in both sexes, although 
the male gonad can often be recognised by its whitish colour, without 
microscopic examination. 
flach gland or gonad is formed by an immense aggregation of richly 
brancbed and minute nicemose lobules, scarcely half-a-millimetre in 
diameter, the ducts from which unite to 
form a short common duct fi'om each gland, 
which oi)ens by a minute aperture close by 
the ureter into the cavity of the inner gill 
within the sin)ra-branchial chamber of its 
side. 
'riiere are no accessory organs develoj)ed 
in connection with the reproductive system, 
and sexual congress is therefore im])ossible, 
and necessitates the social aggregation of 
these mollusks within limited areas to ensure the fertilization of tbe 
ova, as tbe spermatozoa are simiily and freely discharged into the 
surrounding water with tbe exbalent current by the male, and drawn 
with tbe inlialeut water by the branchial siphon into the pallial cavity 
of the female, probably fertilizing the ova while within the gill lamella'. 
I' k;. 3.’)’). — A Loltulc of the 
ticniial gland of Anodonta ana- 
tina^ with its eflerent duct, and 
^ho^ving the developing ova, 
liii;hly magnified (after \’ugt and 
Yung). 
Altliougb, in tlie foregoing pages, 1 have briefly examined examples 
of a typical (fastroi)od and Pelecypod, chiefly from a morphological 
standj)oint, yet tbe various .species (jf our fauna, owing to the 
specialization of habits or function they have undergone, exhibit such 
modifications of their various organs that this phase of our study 
would be incomplete without a fuller account of the organs individually, 
detailing the differentiations in structure and function they each 
undergo, and referihig to the i)bylogenetic and other points of intere.st 
in connection therewith. For this pur 2 ) 0 se I jR’opose to adhere to the 
nietbod 1 have hitherto followed of first treating upon the external 
featui-es and afterwards studying the internal oiganization. 
