Processes of the Echinoderm Egg during Fertilisation. 413 



De Morgan and Fuchs (4), that this species can be readily raised to the 

 sexually mature F 2 generation in the laboratory if a few simple rules are 

 followed in rearing the larvae. 



Methods. 



In making the heat measurements the differential calorimetric method has 

 been adopted instead of the direct method employed by Meyerhof. It requires 

 no expensive fittings or elaborate thermostats, and has the advantage that a 

 number of separate determinations can be made at the same time. All the 

 ■following experiments were carried out so that the eggs were efficiently 

 aerated. This was carried out so as not to interfere with the accuracy of the 

 heat estimations. To test this point many preliminary experiments were 

 made.* All final calibrations were carried out under conditions identical with 

 those of an actual experiment ; the mean of 30 or 40 determinations being 

 taken as the final figure. 



The oxygen and carbon dioxide determinations were carried out by the 

 employment of a special pattern of the Barcroft (5) differential manometer, 

 in which it was possible to fertilise the eggs in the closed chamber of the 

 instrument. It was thus possible to record the oxygen consumption and 

 carbon dioxide output of the eggs while the sperm were actually making their 

 way into the egg. As this instrument and the mode of its use has already 

 been described in a previous paper (6), it is unnecessary to give an account of 

 it here. 



In the heat measurements, the form of differential calorimetric method 

 employed has been that devised by A. V. Hill (7), and has already been clearly 

 described by him at some length. The method is based on the fact that, 

 within fairly wide limits, a vacuum flask may be given any desired rate of 

 ■conduction of heat to the outside by simply increasing or decreasing the 

 volume of its fluid contents. By placing the right quantity of fluid, in this 

 case eggs in sea-water, in one flask, and an appropriate quantity of plain sea- 

 water in another flask acting as a control, the two flasks can be given the 

 same temperature fall. They can then be used in making a differential 

 determination, on being connected with one another by means of a thermo- 

 couple, with one junction in each flask. The thermocouple being in circuit 

 with a delicate galvanometer, any deflection of the mirror gives the difference 

 of temperature between the two flasks. A copper-constantan thermocouple 

 was used in circuit with a sensitive Ayrton-Mather galvanometer. The 



* Aeration was carried out by bubbling a very small volume of water-saturated air 

 simultaneously through both flasks at regular intervals, the eggs in the flask being 

 previously well aerated for 20 minutes before the commencement of the experiment. 



