140 



BIOLOGICAL LECTURES. 



8th pairs of gills, according to Putnam. In the 12 and 13-gilled 

 forms I have found it between the 5th, or at most, the 6th pairs 

 of gill-sacks. 



In the material which I was able to collect at Monterey the 

 following proportions of the several variations prevailed : 



individuals had 1 1 gills on both sides. 



" one side 



" the other side. 



" both sides. 



" one side 



" the other side. 



101 



26 



208 

 ii 



and 

 had 



1 1 



12 



12 

 " 12 



and 13 

 had 13 



both sides. 



354 total number of individuals counted. 



FIG. 7. The olfactory organ 

 seen from its ventral surface. A r , 

 nasal tube. Z, the nasal plates, 

 of which there are three on either 

 side of the median raphe. A'. 

 X 2 diameters. 



FIG. 8. A transverse section of the 

 olfactory organ of Bdellostoma, showing 

 the nasal plates cut across G, and also 

 partly in surface view, S. A 1 , the raphe, 

 and Z, the lateral wall of the nasal cap- 

 sule. X 4 diameters. 



Of the eight 1 1-12 variation, where the position of the gills 

 was noted, four had n gills on the right side and 12 on the 

 left, while the other four were just the reverse, with 12 gills 

 on the right side and 1 1 on the left. The same alternate vari- 

 ation holds true of the 12-13 variation. This fact of alternate 

 variation proves conclusively that the variability in number of 

 gills between the two sides is in no way connected with the 

 formation of the ductus oesophago-cutaneus, which is always 

 upon the left side. 



The vascular system of Bdellostoma is being studied in 

 Prof. Gilbert's laboratory at Stanford University, and I need 

 not enter into the interesting relations which this system of 

 organs sustains to the general variability of this animal, 



