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Twin Gastrulae and Bipinnariae of Luidia sarsi, Diiben, 



and Koren. 



By 

 James F. Gemmill, M.A., M.D., D.Sc. 



Witli Figures Pis. I-III (Figs, 1-21). 



Early in June of this year (1914) I received from the Plymouth Marine 

 Laboratory through the kindness of Dr. E. J. Allen, f.r.s., several 

 Thermos flasks containing quantities of a culture of Luidia in the early 

 blastula stage. This culture was made for me by Mr. James Gray, King's 

 College, Cambridge, to whom, and to Dr. Allen, I desire herewith to 

 express my indebtedness. The larvae were little the worse of the journey 

 to Glasgow, but it seemed to me that they showed even greater irregu- 

 larities of form than might have been expected from Mortensen's (13) 

 description of blastula formation in our species. However, in the end, 

 abundance of perfectly typical young bipinnariae* were secured from the 

 contents of the various flasks. The abnormal larvae became gradually 

 fewer through death, and those which survived could be isolated without 

 much trouble, since they exhibited less capacity for keeping near the 

 surface of the water than their healthier brethren. A great many of the 

 early malformations were of the nature of double or twin formation, 

 and it soon became evident that the teratological type in question, 

 namely, double monstrosity, was about to receive a more varied expres- 

 sion, and to attain a more advanced stage in development, than it had 

 ever before been my good fortune to find in any starfish culture. 



In the accompanying illustrations two series of abnormal larvae are 

 figured, one at the gastrula stage (Figs. 1-11), and the other at that of 

 the early bipinnaria (13-21). As a description is appended to each 

 figure, only questions of general interest need be dealt with here. 



Classification. In the systematic teratology of vertebrates. Double 



* Two points in normal flevelopnient niaj' be noted here. (1) There does not appear to 

 be an auricularia stage in the formation of the bipinnaria, the i)reoral and postoral bands 

 being separated from one another antero-dorsally by a distinct inteival at the time when 

 they are first recognisably differentiated in this field (see 7, p. 232). Indeed, the rela- 

 tively great width of the interval in question would by itself enable us to distinguish the 

 larva of Luidia from those of Astcrias rubcns, A. (jlacialis, and Povania pulvilliis during 

 the first fortnight of bipinnarial life. (2) The small structure arising posteriorly from 

 endoderm and interi>retcd by me as a rudimentary posterior enterocoelic growth in Astcrias 

 rubens, A. glacialis, and Porania pulvillus does not appear to be formed in Luidia (sec 7, 

 p. 233). 



