174: MICROSCOPY FOR BEGINNERS. 



minute rhombic scales covering the back and sides, and 

 by the remarkably long and jointed caudal branches, 

 each of the latter forming from one-third to one-fourth 

 of the entire length of the body. The animal is the 

 largest yet discovered, measuring -fa inch long. The 

 caudal branches are composed of about twenty sections 

 or joints, each of which is slightly constricted. The head 

 is broadly rounded, and formed of three lobes, one front- 

 al and two lateral, the former terminating on each side 

 in a single, acuminate, hook-like process, habitually in 

 close apposition with the anterior region of the lateral 

 lobes, of which the posterior extremities also terminate 

 each in a single hook-like continuation, rather more con- 

 spicuous than those at the front. The mouth is beaded, 

 and has immediately behind it on the ventral surface a 

 deep, narrow, transverse, and slit-like depression, rather 

 less than one-half as long as the diameter of that part of 

 the head. This is the only known Chsetonotus with 

 this problematical feature. 



The back and sides are completely clothed by minute, 

 imbricated, rhombic scales, their front, pointed margins 

 being directed towards the head. They are not more 

 than y^ inch in length, and when examined with a 

 high power (one thousand diameters) they present a 

 beautiful appearance. The lateral margins then seem 

 to be thickened, and the posterior border of each scale 

 appears to bear a minute supplementary scale in the 

 shape of a triangle. 



Although the beginner may not be able to distinctly 



