ON THE DEVELOPMENT OF SOME BRITISH ECHINODERMS. 



for advice. He suggested that we might try to raise the alkahnity of the 

 water by adding some drops of sodium hydroxyde (NaOH). This proved 

 excellent. The spermatozoa at once began to move, and then the fertiliza- 

 tion succeeded completely. It was already at a rather late point of time, 

 the 27th June, so that it could not be expected to get the complete de- 

 velopment of this species ; still a good deal was reached, and as this is the 

 first time a Luidia has been reared, the observations are of some interest. 

 The cleavage is unequal, the relative size of the two first cleavage 

 cells being, however, somewhat variable. The blastula has the same 

 remarkable character as is described by Masterman for Henricia san- 

 guinolenta* and by Gemmill for Solaster endeca,'\ the cell layer forming 



Fig 7. 

 Figs. 7-9.- 



Fig. 8. Fig. 9. 



-Bipinnaria of Luidia ciliaris. 7, five days old ; 8, six days old ; 

 9, eighteen days old. Front view. 100/1. 



irregular folds. The gastrula is rather elongate and large ; this stage 

 is reached on the third day. After five days the larvae begin to assume 

 the shape of small Bipinnarise (Fig. 7) ; the enterocoel vesicles have 

 formed, but the vibratile chord is not yet differentiated at the anterior 

 end. The next day, the 3rd July, the vibratile chord was complete 

 (Fig. 8). The most advanced stage to which the larvae reached before I 

 left Plymouth is represented in Figure 9, from the 14th July. The 

 processes have begun to appear, and the preoral lobe has begun to assume 

 the characteristic elongate shape of the Luidia larva ; the enterocoel 

 vesicles have united in the preoral lobe. 



After my return to Copenhagen I had the pleasure to receive a couple 



* A. T. Masterman, "The early development of Crihrdla oculata (Forbes), with 

 remarks on Echinoderni development" {Trans. R. Soc. Edinburgh, Vol. XL, 1902). See 

 especially Plate 1, Fig. 17. 



t James F. Gemmill, "The development of the starfish Solaster cndcca (Forbes)" 

 {Trans. Zool. Soc, London, X.X, 1912). 



