38 
60 
Fi(i. 59. — Longitudinal and slightly oblique section of If. nana after the invagination of its anterior 
portion: ac., sucker; hi. p., anterior opening of secondary cavity, 1. ext., external wall; 1. int., 
internal wall; pr. cav., primary cavity; ros., rostellum. Enlarged. (After Grass! <k Rovelli, 1892a, 
pi. 3, fig. 17.) 
Fig. 60. — Embryo of JL nana. .Same stage as preceding figure, in cro.ss section at the level of the 
suckers: sec. cav., secondary cavity. Other letters as in preceding figure. Enlarged. (After 
Grass! A Rovelli, 1892a, pi. .3, fig. 18.) 
Fig. 61. — Longitudinal and slightly oblique section of an embryo of II. nana at a stage somewliat 
later than fig. 59: ac., suckers; pr. cav., primary cavity; ros., rostellum; sec. cav., secondary cavity. 
Enlarged, (After Grassi & Rovelli, 1892a, pi. 3, fig. 19.) 
Fig. 62. — Transverse section of an embryo of H, nana at the same stage as preceding figure. Enlarged. 
(After Grassi & Rovelli, 1892a, pi. 3, fig. 20.) 
The second stage^ as observed in the fresh state, still showed the 
cavity, and in the anterior part a deep, narrow, invaginated depression, 
shaped in longitudinal optical section like an inverted Y (^g. 54). At 
this stage, also, there are more or less noticeable four points in which 
ous corpuscles. The cells making up the embryo are at this stage 
irregularly disposed and all A^ery small, except a few which are in 
immediate relation with the tail and primary cavity (lig. 55). Xeither 
in this nor in succeeding stages Avas a subcuticular muscle system 
obsei'A^ed. 
