Gatty Marine Laboratory, St. Andrews. 107 



a stormy period of E. and N.E. winds. In size they were 

 about 13 or 14 millim. long, and thus were much smaller 

 than the examples of Sars, which reached about 31 millim. 

 The long diaphanous preoral lobe was in several curved 

 towards the central fin, so as to bring the attached starfish 

 near the latter. The preoral lobe widened abruptly at the 

 body posteriorly, the longitudinal grooves contracting and 

 bending over, with prominent, frilled, slightly tinted pro- 

 cesses, to join the grooves on the arms. The Bipinnaria is 

 narrowed towards the attached Luidia, which is fixed to it 

 by the ochre-coloured gullet and intestine, and bends towards 

 the frills. The ridges and grooves on the arms are continuous 

 with the longitudinal ridges and grooves on the preoral lobe 

 (PI. II. fig. 10). None of the examples were quite perfect, 

 but ten or eleven arms were visible, so that in all probability 

 there were twelve, as in the examples from Norway. These 

 organs are delicate, and occasionally portions of the tip were 

 constricted off. The margins of the grooves on each arm are 

 thickened throughout, and the tissue is corrugated and 

 granular, as in the ordinary Bipinnaria. 



The preoral lobe is contractile and often shows numerous 

 closely arranged transverse wrinkles on the convex side 

 (PI. II. fig. 10), which alter as waves of contraction pass to 

 and fro over it. Previous authors, indeed, describe circular 

 and longitudinal muscular fibres in its wall. The latter is 

 minutely areolar and granular. Of the two ridges on the 

 preoral lobe one passes up each side of the median fin, the 

 other on each side extending to the tip anteriorly, which 

 forms a fan-shaped expansion with two lateral flaps, the lobe 

 tapering off and forming a somewhat pointed axis, with a 

 slight enlargement within the tip in the centre of the fin-like 

 structure. The median fin has a similar structure, the central 

 axis, however, being larger in proportion. No movement of 

 contained fluid or corpuscles was visible in the enterocoele of 

 the preoral lobe, which disintegrated from the front *. 



The young starfish (Luidia) had reached an advanced 

 stage and appeared to be nearly ready for separation. Groups 

 of granules moved to and fro in the tube-feet, which had 

 thickened cushion at the rounded tips. The paxillae were 



* Dr. E. Metschnikoff (Q. J. Micros. Sc, n. s. vol. xxiv. p. 96, 1884) 

 likewise noticed the tips of the arms breaking off. Besides observing the 

 morphogenetic functions of the wandering cells of the mesoderm (which 

 give rise to the cutis, the skeletal structures, and the oral musculature), 

 he found they had the power of acting on the spherules of milk which be 

 had injected. The rapid disappearance of the parts of the Bipinnaria 

 is probably due to the same agency. 



