Asymmetry in the Plutei o/" Echinus miliaris. 177 



beginning of the development of a right hydrocoele. Then, however, in 

 spite of all our endeavours to keep it alive, the Nitzschia culture, which 

 was used for food, died off, and the development of the Echinus larvae was 

 consequently arrested. In fact, all of those that had been exposed to the 

 action of hypertonic water died, and the larvae in the control culture were 

 given up for lost. But two months afterwards Dr. Ohshima, returning 

 after an absence, found many of these larvae alive and in an advanced state 

 of development, and amongst them he discovered, in addition to a certain 

 number of right-handed larvse, a number which had developed two 

 hydrocoeles. 



The explanation of this phenomenon which I suggest, is that the long 

 period of starvation had checked the normal development of the left 

 hydrocoele, so that this had remained small, and when conditions improved 

 the innate tendency of the right side to develop a hydrocoele was no longer 

 inhibited by too great a development on the left side. 



If this explanation is justified in Dr. Ohshima's specimens, the right 

 hydroccele would have been produced by the mgative metlwd of checking 

 the development of the left side, whilst in my earlier experiments it was 

 produced by the positive method of direct stimulation of the right side. 



Dr. Ohshima quotes an observation of Eunnstrom's to the effect that 

 a larva had been observed by him devoid entirely of a hydrocoele, but with 

 pedicellariffi developed on both sides. I suggest that Eunnstrom has over- 

 looked the presence of vestigial hydrocoeles in this larva. As I proved 

 in 1918(6), when larvte are starved so that the hydrocoele rudiment is 

 completely absorbed, they develop pointed spines on both sides, but no 

 pedicellariae. I too, like Eunnstrom, imagined that I had found larvas with 

 pedicellarise on both sides, but no hydrocoele ; but these, when mounted 

 whole and closely examined, disclosed minute hydrocoeles on both sides. 



EEFEEENCES. 



(1) Conklin, E. G., 1903. " The Cause of Inverse Symmetry," ' Anat. Anz.,' vol. 23, 



Nr. 23. 



(2) Gemmill, J. F., 1915. " Twin Gastrnlfe and Bipinnarije of Luidia sarsi," ' J. Mar. 



Biol. Ass.,' vol. 10, No. 4. 



(3) Id^m, 1916. " Double Hydrocoele in the Development and Metamorphosis of the 



Larva of Asterias rubens," ' Q. J. M. S.,' vol. 61, No. 241. 



(4) Grave, C, 1911. "Metamerism of the Echinoid Pluteus," 'Johns Hopkins Univ. 



arc.,' No. 232. 



(5) MacBride, E. W., 1911. " Two Abnormal Plutei of Echinus, etc.," ' Q. J. M. S.,' 



vol. 5", No. 226. 



(6) Idem, 1918. " The Artificial Production of Echinoderm Larvje with Two Water- 



Vascular Systems, etc.," ' Eoy. See. Proc.,' B, vol. 90. 

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