THE DEVELOPMENT OE ASTERINA GIBBOSA. 289 



Figs. 87 and 88. Two sections of a larva between Stages D and E. 

 pV., s^V. Pore-canal and stone-canal of right side in connection 

 with normal right hydrocoele, r. hy. Their openings into this are 

 in another section, r'%'. A second, more ventrally situated hydro- 

 coele rudiment on the right side, with a distinct opening into coelom. 

 The left hydrocoele is feebly developed for the stage which the larva 

 has reached, and has only four lobes. 

 I'ig. 89. Section of a larva of Stage D, in which the right liydrocoele has 

 five lobes, and is larger than the left. This section is drawn from the 

 ventral aspect, and hence appears reversed, 

 fig. 90. Section of a larva of Stage G, showing a " collar pore " opening 

 from the left hydrocoele between lobes 2 and 3, directly to the exterior. 

 Figs. 91—94. Four sections of an almost normal larva of Stage E, or 

 somewhat older. ^. e. Normal pore-canal, opening into axial sinus, 

 the septum between the latter and the left posterior coelom being 

 still incomplete dorsally. p' . d. Pore-canal, st' . d ., and stone-canal in 

 connection with the right hydrocoele. Pig. 93 shows the opening of 

 the second pore-canal into the axial sinus. Eig. 92 shows the opening of 

 the second stone-canal into the right hydrocoele. Y\%. 91 shows the two 

 pore-canals uniting to open by a common pore. (Compare Woodcut 3.) 

 Fig. 95. — Section parallel to the larval plane from larva of Stage C, showing 

 the first trace of right hydrocoele. (Compare Plate 19, fig. 35.) Note its 

 relationship to the anterior ccelom, which extends obliquely beyond it pos- 

 teriorly, passing under it and to the right of it. Magnification 1000 diameters ; 

 Leitz's immersion -j^-. 



Figs. 96 and 97. — Two sections of body-wall of young star-fish, cut per- 

 pendicular to disc, in which R equals '8 millimetre. Fig. 97 shows first trace 

 of "papula" or dermal branchia (Ar«K(;A.). Fig. 96, origin of its peribranchial 

 space, p.br. Magnification 400 diameters. 



Fig. 98. — Section of body-wall of young star-fish, in which R equals 

 •88 millimetre, showing dermal branchia and its peribranchial space. Mag- 

 nification about 400 diameters. 



PLATE XVII. 



Figs. 99 — 106 illustrate the development of the so-called heart or " ovoid 

 gland." The sections represented are perpendicular, or nearly so, to the 

 disc of the star-fish, and the magnification is 350 diameters. 



Fig. 99. Section of larva of Stage G. ov.g. Fold projecting into the 

 axial sinus, the rudiment of the ovoid gland, pr. germ. inv. Invagina- 

 tion of peritoneum, whence the primitive germ cells are formed. Calc. 

 Calcigenous tissue in the body wall. 

 Figs. 100—103. Four sections of a specimen older than preceding. Fig. 

 101 show« the growth of the primitive germ cells into the rudiment 



