50 DE. J. r. GEMMILL ON THE DEVELOPMENT OE 



apparently healthy. Since the end of metamorphosis, however, their growth has been 

 very slow. Probably the tanks do not afford them the proper kind of food, all that is 

 available being the fine growths of algae present on the sides and some granular debris 

 which has settled to the bottom. I hope later to have the opportunity of making 

 experiments with a view to finding out what their natural food may be, and of rearing 

 them through further stages in early growth. 



So far I have been quite unable, in examining material dredged up from likely 

 iSolaster ground at Millport, to come across examples either in metamorphosis or in 

 the stages that immediately succeed it. 



Of the two glass vessels containing young larvae which I took with me to Glasgow, 

 one had a capacity of half a gallon and the other rather less. Both were shaded 

 and kept under gentle continuous aeration by means of an aerating apparatus 

 (8) devised by me in connection with an earlier attempt at the rearing of Solaster. 

 From time to time a little fresh water was added to make up for the loss caused by 

 evaporation. Development proceeded in a perfectly normal manner, but with some- 

 what greater rapidity than at the Station, owing no doubt to the difference in temperature 

 of the laboratory in Glasgow and the sea-water at Millport. The living specimens in 

 these aquaria, being always at hand, proved of the greatest use for purposes of 

 general observation. 



I am much indebted to the Superintendent, Mr. Richard Elmhirst, and the Staff of 

 the Millport Station for the ready and careful manner in which they assisted me all 

 through in the work of obtaining and rearing the larvse. My best thanks are also 

 due to Mr. Alex. Gray, formerly Curator of the Station, with whose good help a 

 first and practically successful attempt at the work was made several years ago. 

 Acknowledgment is also due to Mr. Jas. A. Boyle, Art Master at Hillhead High 

 School, Glasgow, for much expert assistance in the finishing of the Plates. 



X. Summary of chief Features in Development of Solaster. 



(For paging, see under Contents, p. 1.) 



(A) Externally. 



Egg floating, flattened at upper and lower poles, the latter paler in colour ; seg- 

 mentation total, equal ; blastula formed by egression of the central cells along numerous 

 lines, and gastrula by invagination at lower pole. 



Closure of blastopore ; no formation of larval mouth ; a long free-swimming stage ; 

 "larva" with three glandular arms and a disc-shaped sucker; for a time, perfect 

 external symmetry except for hydropore on right side. 



Flexion and torsion of preoral lobe towards left side; stage of attachment by the 

 larval sucker; reduction in size of preoral lobe, and incorporation of much of its 

 epiderm with the oral surface of the Starfish ; metamorphosis occurring in such a way 



