21 



THE NAUTILUS. 



largest young one found within the brood pouch. Several 

 nine-millimeter specimens were sectioned' but none were found 

 to contain young. Young six, seven, and eight millimeters 

 long have sex organs fully formed. I have no sections of very 

 small Calyculina. The young of this form within the parent's 

 gills are in the same stages of development as to the sex organs, 

 as those of Sphaerium. 



In the table which follows are included the results of gross 

 examination of a number of Sphaeria. This is incomplete, 

 since it was not possible to determine the presence of any young 

 under five tenths of a millimeter. The animals examined were- 

 taken during July, 1913. 



Size Total Total Percentage 



Length in mm. Examined Bearing young Bearing Young 



7 



3 



0 



0 



8 



12 



0 



0 



9 



27 



0 



0 



10 



21 



0 



0 



11 



30 



0 



0 



12 



45 



0 



0 



13 



30 



2 



6.6 



14 



40 



10 



25 



15 



47 



22 



46.8 



16 



64 



51 



80 



17 



64 



53 



83 



18 



14 



14 



100 



19 



4 



4 



100 



Sphaerium Bearing Young over 



.5 mm. Long. 



Size 



Number bearing 



Total of 



Per cent of 



young 



class 



class 



13 



2 



30 



6.6 



14 



10 



40 



25. 



15 



22 



47 



46.8 



16 



51 



64 



80. 



17 



53 



64 



83. 



18 



14 



14 



100. 



19 



4 



4 



100. 



