On ihe Development of a a Asterid. 387 



XLIV. — Some Observations on the Development of an 

 Asterid with Large Yolky Egys from the Franklin Islands. 

 By E. H. Henderson, M.Sc, M.D., McGill University, 

 Montreal*. 



[Plates XII. & XIII.] 



The material consisted of a brood of young starfish collected 

 ofif the Franklin Islands and belonging to the British 

 Museum, and the work was carried on in the Zoological 

 Laboratories of McGill University during the summer 

 vacations of the years 1902-03-04. 



External Appearance. — On examination the specimens 

 showed evidence of being in the fixing stage, being aggluti- 

 nated together into masses resembling miniature bunches 

 of grapes. The five-rayed shape was in all cases evident 

 and at first sight seemed to be due in part to the pressure of 

 neighbouring embryos on each other, but on closer exami- 

 nation Mas seen to be really due to the assumption of that 

 typical form of the adult starfish. 



When one of these masses was separated with a needle 

 into its constituent members and examined under a hand- 

 lens, it became evident that the individual members were 

 connected together in the region of the preoral lobe (this 

 arrangement giving them that peculiar bunched appearance), 

 the preoral lobes being central, while the dorsal portions of the 

 embryos were outermost. 



The individuals themselves were of large size, measuring 

 almost 2 mm. in diameter ; they were hemispherical in shape, 

 the ventral surface being flat and showing the radial sym- 

 metry, the dorsal surface dome-shaped. There were only 

 two or three members of the collection which did not show 

 radial symmetry, and these proved to be only masses of 

 yolk surrounded by a membrane, very likely unfertilized 

 eggs (PI. Xir. fig. B). 



PI. XII. fig. A shows a group of three, from which others 

 have been detached, so as to reveal the characteristic union 

 of the preoral lobes. 



PL XII. figs. C and D are drawings to represent what were 

 the earliest stages in the collection. The preoral lobe is still 

 prominent, showing little or no constriction, while the 

 hydrocoele is just appearing as two longitudinal ridges in each 

 radius. The five-rayed appearance is seen only from the 



* Abstract of a thesis presented for the M.Sc. degree. 



26* 



