A PAIR OF CLAMS. 



Once upon a time two tiny specks of 

 clam life, too small to be seen with the 

 naked eye, found themselves started upon 

 a strenuous, and as it proved, adventure- 

 some career, for their phlegmatic race. 

 They were not alone, these specks, nor 

 unprotected. Scores, yes, hundreds of 

 them were in the brood. Mother Clam, 

 though she had no wings, had gills that 

 served the same purpose for her young. 

 In the outer pair of the four plate-like 

 gills were little cavities reached by small 

 openings. Through these ran currents of 

 water for food and respiration, and these 

 currents swept the little clam eggs into 

 safe brood-chambers. The gills were 

 then much swollen by their burden. Now 

 all of this might have happened in almost 

 any lake or stream we are familiar with 

 any spring. But as a matter of fact, 

 these particular specks began existence in 

 a stream in Indiana, several seasons ago. 



The little eggs now began rapidly to 

 develop. First, like all eggs, each was 

 just one cell of that universal, mys- 

 terious stuff, the ground work of all ani- 

 mal and plant life, protoplasm. Through 

 some mysterious directing force with 

 them each cell divided into two; these 

 two into four, and so on, until there were 

 many cells with a membrane, some larger 

 than others, and surrounding a hollow 

 center. Then one side pushed itself in, 

 as 3^ou would push in one side of a rub- 

 ber ball to make a double walled cup. 

 Out of these two layers and a middle one 

 formed from them, grew all of the tissues 

 of the adult body; each cell although in 

 looks exactly like the others, always 

 forms the same part. First of the organs 

 to be formed was a little gland, a tiny 

 unfolding of the surface. This gland 

 secreted a little shell, covering what was 

 destined to be the upper side of the 

 bodv. But this embrvonic shell was 



short-lived. It was soon replaced by a 

 bivalve or paired shell, a strong family 

 character. But it differed considerably 

 from the adult shell so familiar to us all. 

 It was triangular, and on its lower edge 

 were incurved hooks beset with spines, 

 the use for which appeared later. And 

 next a change came which would have 

 enabled us, had we been there, to recog- 

 nize in these mites some semblance to 

 the adult clam. The mass of embryonic 

 cells lying between the shells became 

 divided by two clefts from below into a 

 central mass, destined to be the body 

 with its organs, and on each side a plate 

 or sheet which fitted the shell of that 

 side grew more and more to look like the 

 thin skin or mantle of an adult mollusk. 

 On these mantle lobes grew little brushes, 

 which were really sense organs. Some 

 of the cells of the middle of our original 

 rubber ball had been forming a muscle 

 which ran from shell to shell. On the 

 lower or ventral side of the body might 

 then be seen a peculiar gland whose 

 secretion formed a long thread called a 

 byssus. Our larval clams w^ere entangled 

 with their fellows by these threads in the 

 brood pouches, and nourished by secre- 

 tions from their walls. 



Anyone looking at the enlarged gills 

 of Mother Clam at this time might have 

 thought them quite stuffed with sand 

 grains ; but these sand grains were soft 

 and very much alive, and quite complex, 

 as a microscope would have shown. They 

 were now ready to shift for themselves ; 

 one day they were ejected by the water 

 currents from their cradles and thrown 

 out into the world, at the tender mercy 

 of wind and waves and living creatures, 

 to prove in competition with them of 

 what stuff they were made. Not all baby 

 clams can possibly live. If they did, 

 the rivers would in time be packed with 



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