370 Grant Sherman Hopkins 



veins is in the large caudal vein which extends along the ven- 

 tral side of the axon. The tail may be cut off a little cephalad 

 of the base of the caudal fin and the canula easily inserted 

 into the vessel. But as the caudal vein sends off branches 

 into the kidneys, which either break up completely or par- 

 tially in this organ, the further precaution must be taken to 

 use for injecting some mass that will pass through these small 

 vessels into the cardinal veins be3^ond. Such a mass may be 

 made by taking lo grams of gelatin and adding 50 c. c. of 

 water ; this is melted over a water-bath and 150 c. c. of water 

 colored with Berlin-blue, is added. This mass becomes fluid 

 at such a low temperature that there is little danger of the 

 gelatinization of the connective tissue of the blood-vessels and 

 their consequent rupture, when injected, as would be liable to 

 occur if the injecting mass melted only at a comparatively 

 high temperature. For injecting the lymphatics, the follow- 

 ing mass serves very well. Gelatin, 20 grams ; water, 200 

 c. c. ; potassium dichromate, sat. aq. sol. 75 c. c. ; acetate of 

 lead, sat. aq. sol. 75 c. c. The gelatin is melted over a water- 

 bath ; the hot dichromate is then added after which the hot 

 acetate of lead is added and the whole mass filtered through 

 flannel or absorbent cotton. 



I^ATERAI, LINE, LATERAL OR MUCOUS CANAL AND LATERAL LYMPHATIC 



VESSEL. 



In order to avoid any possibility of misapprehension in re- 

 gard to these three terms it has been thought well to briefly 

 describe them. The lateral line is a longitudinal line along 

 each side of many fishes, marked by the structure or color of 

 the skin, or both. It consists of a row of tubes or pores, 

 mostly on scales, extending from the head to or toward the 

 tail. The pores are the ducts of muciferous glands whose 

 product is excreted on the sides of the fish. (Cent. Diet). 



Lateral or Mucous Canal. — In most, if not all, fishes the in- 

 tegument of the body and of the head contains a series of sacs, 

 or canals, usually disposed symmetrically on each side of the 

 middle line, and filled with a clear gelatinous substance. . . . 

 These sensory organs are known as the ' 'organs of the lateral 



