Clisetoptems Variopeclatiis. 515 



Anterior region. — The anterior region comprises abont two-thirds 

 of the larva. It lacks the flagella of the earlier stages and its gen- 

 eral ciliation has begun to undergo atrophy. The mouth and the 

 esophagus, however, retain the strong close-set cilia over their sur- 

 face. The mouth has undergone further axial enlargement by a 

 slight increase in size and further tilting of the pre-oral lobe so that 

 its free ventral margin is nearly in an horizontal plane instead of 

 transverse to the axis of the body. The post-oral lobe, which has 

 increased in length by a growth at its margin, resembles a protruded 

 tongue. The eye-spots on the pre-oral lobe are the same in number 

 and position as in the stage just described (Fig. 10). 



Nine short transverse rows of brownish-red pigment spots, on each 

 side of the median line, mark off a shield-shaped area on the ventral 

 side of the anterior region between the base of the post-oral lobe 

 anteriorly and the foremost ciliary ring posteriorly. Each line of 

 pigment-spots corresponds with the position of the setse in the next 

 stage. 



Middle region. — The middle region is that portion of the larva 

 which begins with the foremost ciliary ring and ends at the ill- 

 defined constriction just anterior to the anus. It consists of two 

 ciliary rings and three more or less clearly defined segments which 

 decrease in size regTilarly toward the anus. 



The ciliated rings are referred to in this paper as ''first," "second," 

 and ''third" to designate their order of development. The second 

 and third rings consist of a row of powerful cilia on a thickened 

 ectodermal ring that surrounds the widest portion of the body, 

 excepting for a short space on the mid-ventral side of the larva 

 (Fig. 10). 



Posterior region. — This region of the larva consists of a very 

 short anal segment to which the growing zone is confined. Its diam- 

 eter is scarcely more than the anus itself. 



The "holdfast" may be regarded as a part of the anal segment 

 from which it is a ventral outgrowth, and into which it is contracted 

 in the transformed larva^. -When the animal is attached to a firm 

 substance, as the Ixittom (if a \vatch-i>hiss, a considcvalile decree of 

 agitation of the watcn* is required to detacli it. In tliis, nnd several 



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