i6 
THE NATURALISTS’ JOURNAL. 
I was about to adopt, except for the absence of functional 
reproductive organs. In the beautiful language of my his¬ 
torians and biographers, I was ‘ a bilaterally symmetrical 
animal.’ 
“ I found my two adductors very strong and serviceable, 
and as my shell enlarged, so equivalently did they. At the 
narrow end of my shell—the posterior—were two syphons 
tentacularly fringed, which by their constant motion induced 
currents carrying all kinds of food into my mouth, such as 
diatoms , desmids , algce , &c., thus serving at once the double 
purpose of nourishment and respiration. I dare say you have 
noticed me as I lay obliquely in the mud, with my posterior 
end upwards, disclosing the syphons, and you have also, per¬ 
haps, wondered at their extreme sensitiveness to the least 
disturbance in their vicinity, when you have seen them sud¬ 
denly disappear and the valves close tightly together. Yes, 
sensibility is one of my chief characteristics—in this part, at 
least, as you will admit—and the greater amount of develop¬ 
ment my syphons undergo bears directly on the question of 
the higher or lower development of my retractor muscle.* 
“ And now I must tell you a little about my present noble 
shell. From the moment I dropped from the fish to the quiet 
bottom of the pool I commenced to grow. Little by little 
additions were made to my shell, each successive addition 
being marked by a separate and distinct line following the 
general contour of my foundation shell. As my shell ap¬ 
proached maturity, the lines began to approach closer to¬ 
gether until finally they nearly merged into each other, for 
the amount of additional matter grew smaller. Some little 
disagreement appears to exist among my biographers as to 
the method of formation of my shell. It is generally regarded 
as a cuticular secretion of the mantle ; the cells at the edge 
forming the epicuticula ; those of the part adjoining the pris¬ 
matic layer, and those of the general surface the nacreous 
layer; for you must understand that my shell consists of three 
layers, and here ” said the swan mussel turning to the 
Sphcevium covneum , “ I differ from you, for you have no pris¬ 
matic layer.” The Sphcevmm covneum shrank back abashed 
before the majestic looking Anodonta , who continuing said 
“ but then we cannot all hope to be swan mussels and I do 
not despise you for not being one, I only pity you. As I was 
saying—or about to say—the epicuticida or peviostvacum is 
purely of organic structure, composed of a substance termed 
concliiolin like the organic substratum of the rest of the shell. 
It is of a horny consistence and laminated and the ridges on 
* Retractor pedis. 
