208 TRANSACTIONS OF SECTION D. 



served as food for the larvae, to grow in the hypertonic sea-water. 1 natuially 

 supposed that, had I been able to accomplish this, I should have obtained a 

 much larger proportion of larvae with a double hydrocoele. In 1919, accordingly, 

 I instituted experiments with a view of attaining this end. I succeeded in 

 obtaining a strain of Nitischia which grew luxuriantly in hypertonic water; 

 and three large cultures were instituted in bell-jars of 30-litres capacity, 

 each fitted with a Browne plunger. In one of these there was normal sea-water, 

 in which larvae were placed which had never been exposed to hypertonic water ; 

 in another there was hypertonic sea-water containing larvae which had been 

 in this medium since they were three days old ; and in the third there was 

 normal sea-water in which were larva; which had been exposed to hypertonic 

 water for eleven days — viz., from the time when they were three days old until 

 they were fourteen days old. The result of these experiments was as follows : — 

 In the jar containing larvae which had never been in hypertonic sea-water no 

 specimens with two hydrocceles were found; in the jar filled with hypertonic 

 sea-water one specimen with two hydrocceles was found ; whilst in the jar 

 containing larvae which had been in hypertonic water for eleven days 4 per cent, 

 of the larvfe were provided with two hydrocceles. In all three jars the larvae 

 were exceedingly vigorous, and many of them completed their metamorphosis. 

 Unfortunately, owing to the premature removal of the larvae with two hydrocceles 

 to a srraller vessel in which they did not flourish, none of them completed the 

 metamorphosis, but this is not impossible, as I possess one larva obtained from 

 a pre-war culture which actually accomplished this feat. 



The conclusion to be deduced from these experiments is that retransferring 

 the larvae to normal sea-water after they have been exposed to hypertonic 

 sea-water is an essential part of the process of producing a double hydrocoele. 

 I hope next spring to be able to determine the length of exposure to the action 

 of hypertonic sea-water which gives the optimum result. The question as to 

 what is the reason of this necessity is not easy to answer. Of course, when 

 Loeb used hypertonic sea-water to stimulate the development of unfertilised 

 eggs, he fomid that there was a certain optimum time of exposure to this 

 medium, but in this case too long exposure checked development and gave rise 

 to only abnormal and sickly larvie. But the larvae of Echinus miliaris flourished 

 exceedingly in hypertonic sea- water; and Loeb's explanation is therefore not 

 available. I can only tentatively suggest the following : — The exposure to 

 hypertonic water acts on a hidden rudiment in the larvte and starts the right 

 hydrocoele developing. But I have already shown, in my Eoyal Society paper, 

 that the organs developing on one side of the larva tend to inhibit the develop- 

 ment of similar organs on the other side. So, when the proper hydrocoele on the 

 left side begins developing and gets a long start over its right antirnere, it may 

 check and eventually entirely suppress the development of this. The retrans- 

 ference to normal sea-water may possibly hold up temporarily the exuberance 

 of development of the left side and allow the right side to hold its own. 



If this supposition be well fomided, Echinoderm development would afford 

 a striking instance of that ' struggle between the parts ' on which Roux has 

 always insisted as an important feature of development. 



In conclusion, I should like to say a word about the water used in these 

 experiments. In performing the experiments, the results of which were given 

 in my paper read to the Royal Society, I used sea- water collected at Lowestoft 

 and sold by the Great Eastern Railway for bathing purposes. The distribution 

 of this water ceased early in 1918. I tried artificial sea-water made with 

 Tiedmann's sea-salt, but found that, although NitzscJiia flourished in it, it 

 was instantly fatal to both adult urchins and larvte. I then had artificial 

 sea-water made by the formula given by Dr. Allen (Journ. of M.B.A., vol. 19), 

 and found that it answered admirably, for the larvae flourished in it and 

 completed their metamorphosis in it. The fertilisation of the eggs, however, 

 was effected in sea-water sent from Plymouth. 



2. (a) Leptospira icterohfemon-hagias from the Kidney of local Rats. 

 (6) Spirochceta (? v. sp.) from Guinea-pig . By Dr. A. 0. Coles. 



