occupy a lateral location, and between them a bare space remains on each 

 side of the body which is considerably larger on the dorsal side and smaller 

 on the ventral side. The posterior zone occupies the entire end of the body 

 and is somewhat more powerfully developed on the dorsal side. The number 

 of cells which compose it is about 17 of which 10 lie on the dorsal side. All 

 in all the ciliary covering of the larva consists of 61 to 62 cells. 



The attaching disc of the larva is almost not delineated from 

 the body; it bears 16 edge hooks of the typical shape for the genus (Fig, 

 192), 0, 010 - 0. 012 mm in length. Each hook is equipped with a well- 

 developed little loop and a thin tendon. In addition to the edge hooks, 

 two little parentheses of 0. 007 mm in length, which apparently represent 

 the inceptions of the first pair of nniddle hooks, are visible somewhat closer 

 to the anterior end of the body. These little parentheses are not visible in 

 all preparations and have very indefinite contours, consequently we hesitate 

 to state with conviction that they are nniddle hooks. 



D.OIhm 



The inner organization of the larva in preparations has not been 

 sufficiently studied. Strongly developed eye spots are clearly apparent. 

 There are three of them--one pair of the anterior and one large posterior 



spot fused from two halves, which is 

 equipped with light refracting little 

 lenses on both sides. The anterior 

 eyes have a diameter of about 0. 005 

 mm whereas the posterior eye is 

 about 0. 01 mm in length and has a 

 width of 0. 03 mm. The light-re- 

 fracting little lenses are about 0. 003— 

 to 0. 004 mm in diameter. The 

 pharynx which lies behind the pos- 

 terior eye is slightly elongated 

 (sagittally, nobis) and is about 0. 015 

 to 0. 017 by 0. 012 to 0. 014 mm in 

 size. The inception of the intestine 

 is not visible in the larva. Further development is not known. Among the 

 larvae impregnated with silver, attention is drawn by several strongly 

 light-refracting bodies (with a diameter of about 0.001 mm) the edges of 

 which are blackened with silver, these are symmetrically distributed in 

 the body (close to its dorsal side). Their number is very considerable 

 (more than 40) but it is not possible to say what they are without further 

 special study. 



,^£i»=> 



Fig. 192. Tetraonchus monenteron 

 (Wagener), attaching armature of a 

 free -swimming larva. 



187 



