340 Prof. E. W. MacBride. The Artificial Production of 



usually occupied by one of the pedicellariae. Such larvae are represented in 

 figs. 12, 13 and 14, and sections of one are shown in figs. 22 and 28. 



In 1915 I possessed a very thick culture of larvse in a Breffit jar ; the 

 larvae were between six and seven days old, and had had as yet no food, and 

 the well-known signs of degeneration were beginning to appear in many of 

 them. The whole contents of the Breffit jar were then added to a plunger 

 jar in which there was a rich culture of Nitzscliia. A few weeks later the 

 plunger jar was seen to be filled with a vigorous culture of advanced larvae, 

 which, to the naked eye, seemed to be completely normal. All had the fvill 

 complement of eight arms and four ciliated epaulettes. When these larvae 

 were examined with a lens about one-third of them appeared to be laden 

 with a mass of calcareous growth on both sides. For a brief moment I 

 thought that my hopes of producing a large number of larvae with a double 

 Echinus-rudiment had been fulfilled ; but when tliese curious larvae were 

 sectioned no trace of hydrocoele could be discovered on either side of the 

 stomach ; nor was there any vestige of a madreporic pore or of a stone-canaL 

 The coelom liad been divided into anterior and posterior portions on each side^ 

 but on neither side was the anterior division enlarged so as to form an axial 

 sinus. Dorsal to the oesophagus a median sac, no doubt homologous with 

 the madreporic vesicle, was discovered {mv., fig. 22). Within the loop of 

 the ciliated band {cil., fig. 23), where normally the amniotic invagination is 

 formed on the left side, there was situated on both sides a group of pointed 

 spines {r.sp., l.sp., fig. 23), and dorsal to this loop, in the position usually 

 occupied by the dorsal pedicellaria on the right side, there is situated on both 

 a pointed spine {r' .sp'., V .sp'., fig. 23). 



These spines differ from those present in the normal larvee in two respects.. 



(1) If we compare them with the spines normally developed on the right- 

 side by the plates which bear the pedicel larite, then we may notice that 

 whereas the spines in normal larvse have square ends with diverging points 

 (resembling somewhat in shape old church-towers), the spines in these 

 abnormal larvse are pointed. 



(2) If we compare them with the spines which in the normal larva are 

 borne by the Echinus-rudiment alternating with the primary tentacles^ then 

 it is to be noticed that the spines of the normal larva are pointed, but are 

 encircled at their bases by a collar consisting of nervous tissue above and 

 muscular tissue beneath, whereas the spines of these abnormal larvse are 

 totally devoid of such a collar. 



In 1916 and 1917 the experiment which I have jiist described was repeated 

 and the same result obtained. Amongst all the larvse which were sectioned 

 one was discovered which possessed a madreporic pore. 



