In the Leptolinae the otocysts are seen in their first stage in _Mitrocoma annae_ (fig. 31) and _Tiaropsis_ (figs. 29, 30) as an open pit at the base of the velum, on its sub-umbral side. The pit has its opening turned towards the sub-umbral cavity, while its base or fundus forms a bulge, more or less pronounced, on the ex-umbral side of the velum. At the _fundus_ are placed the concrement-cells with their conspicuous otoliths (_con_) and the inconspicuous auditory cells, which are connected with. the sub-umbral nerve-ring. From the open condition arises the closed condition very simply by closing up of the aperture of the pit. We then find the typical otocyst of the Leptomedusae, a vesicle bulging on the ex-umbral side of the velum (figs. 32, 33). The otocysts are placed on the outer wall of the vesicle (the fundus of the original pit) or on its sides; their arrangement and number vary greatly and furnish useful characters for distinguishing genera. The sense-cells are innervated, as before, from the sub-umbral nerve-ring. The inner wall of the vesicle (region of closure) is frequently thickened to form a so-called "sense-cushion," apparently a ganglionic offshoot from the sub-umbral nerve-ring. In many Leptomedusae the otocysts are very small, inconspicuous and embedded completely in the tissues; hence they may be easily overlooked in badly-preserved material, and perhaps are present in many cases where they have been said to have been wanting. [Illustration: After O. and R, Hertwig, _Nervensystem und Sinnesorgane der Medusen_, by permission of F. C. W. Vogel. FIG. 34.--Tentaculocyst (statorhabd) of _Cunina solmaris_. n.c, Nerve-cushion; end, endodermal concrement-cells; con, otolith.] [Illustration: After O. and R, Hertwig, _Nervensystem und Sinnesorgane der Medusen_, by permission of F. C. W. Vogel. FIG. 35.--Tentaculocyst of _Cunina lativentris_. ect, Ectoderm. n.c, Nerve-cushion. end, Endodermal concrement-cells. con, Otolith.]