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cent-rated sea water, he treated the egg with certain acids all 

 belonging to a well-defined chemical group he got the formation 

 of the clear membrane. The acids which he found he could use 

 with success were the following: — carbonic acid, formic acid, 

 acetic acid, propionic acid, and butyric acid. All these, except 

 the first one, belong to a group known to chemists as monobasic 

 fatty acids. There are a large number of others much rarer and 

 not so well known. 



The process in detail is this : — He takes a certain concentra- 

 tion of butyric acid in sea water. He adds two cubic centimetres 

 of a very weak solution of butyric acid to 50 cubic centimetres of sea 

 water, and places the unfertilized eggs of the sea urchin in this 

 mixture for about two minutes. He then puts the eggs in con- 

 centrated sea water, 60 per cent., for from 40 to 60 minutes at 

 ordinary temperatures. He next takes the eggs out of that and 

 places them in normal sea water. Directly after they have been 

 taken out of the butyric acid solution they form the clear mem- 

 brane, but the cell does not yet begin to divide. He then places 

 the eggs in concentrated sea water for 40 to 60 minutes, and next 

 into the ordinary sea water, and in half an hour the cell begins to 

 divide perfectly normally into 2, 4, 6, 8, 16, 32, and 64 cells, and 

 so forth. The embryos formed by this artificial fertilization are 

 perfectly normal. They form skeletons perfectly normally ; they 

 swim at the surface of the water normally; and, quite recently, 

 they have been raised to the stage of adult sea-urchins by 

 Delage, of Paris, to whom very great credit is due for the 

 inexhaustible patience he exercised during the two whole years he 

 was nursing these sea-urchins every day. When you realize that 

 one of those almost microscopic embryos, about the size of a pin's 

 head, has to be placed in about five gallons of sea water, supplied 

 with air bubbling through it all the time, and with sterilized 

 diatoms for its food daily, besides having to have the water 

 changed daily, you may realize that some patience had to be 

 expended over the problem of bringing up these fatherless 

 urchins to the adult stage. 



Let us follow the process of the membrane formation a little 

 more closely — the formation of the clear white membrane around 

 the egg cells. If Ave watch the sea-urchin eggs very closely 

 during the first period following fertilization, whether natural or 

 artificial, we observe the following phenomena. First of all we 

 have a normal egg cell of a perfectly spherical, smooth outline, 

 but during the first instants of fertilization sundry little blisters 

 appear on the surface. Little globules float to the surface of the 

 egg and raise a very fine membrane from the surface. These 

 little globules are formed all over the surface of the egg. They 

 get larger and larger until they encroach on each other, and finally 

 fuse into one complete layer all round the egg. You may enquire 

 what happens if this process is allowed to go on. In natural 

 fertilization it does not go on. The clear membrane being once 

 formed, the cell division starts, and the whole thing goes on 

 normally, but by artificial fertilization we separate these two 

 things. We make the membranes first and cause the cell division 

 afterwards. If we let the egg go at the stage where the membrane 

 is formed, and do not proceed any further, what happens ? The 

 egg very rapidly dies. It does not stop at this stage of forming 

 globules on the surface and letting them run into one membrane, 

 but forms globules all through, and finally falls apart and nothing 

 is left. The cell is completely liquefied, or some constituent of 



