344 H. M. Vernon 



which had developed therefrom after twenty-four liours' growth were 

 always carefully counted. This coiiuting was done very simply by 

 thoronghly stirring iip tlie jars of water containing the ova and 

 blastulae, and then withdrawing 3 cc. of tbe water with a pipette, 

 and rimning it into a small glass cell, into wbicb a single drop of 

 saturated corrosive sublimate had previously been introduced. A cover 

 slip was then slid on the top of the cell, and after waiting a few 

 minutes to allow the ova and blastulai to settle, it was fixed in a 

 mechanical stage, and its whole area worked carefully through under 

 the field of the niicroscope. By making these observations after 

 twenty-four hours' growth, one can determiue at the sanie time botb 

 the number of blastula and the uumber of ova which have remained 

 unfertilised, or have not developed uormally to the blastula stage. 

 In each case two separate couutings were made, and a mean taken. 

 If these two values differed at all largely, a third counting was 

 made. In the table at the end of the pa})er are given in each case 

 the number of ova present in 10 cc, the percentage numbers of these 

 ova which had developed to the blastula stage after twenty-four hours 

 growth, and the number of plutei formed after eight days growth. 

 These latter numbers are also the means of two separate countings, 

 made in a similar mauner to those of the ova and blastulse. For 

 further details as to the inethod of making and carrying out these 

 artificial fertilisations of Echinoid ova, the paper mentioned above 

 may be cousulted. 



The chemical side of the investigation consisted in making 

 determinations of the free and the organic or so-called albuminoid am- 

 monia present in the various specimens of water. The method adopted 

 was that of Wanklyn and Chapman*. It consisted in distilling half 

 a litre of the water under examination, and collecting the distillate 

 in tali cylindrical glasses in separate volumes of 50 or 100 cc. To 

 each 50 cc. of distillate, 2cc. of Nessler's reagente a strongly alkaline 

 solution of mercurie iodide in potassium iodide, is added, and the 

 brown colouration thereby produced determiued in terms of a standard 

 solution of ammonium chloride, to whieh the Nessler reagent has 

 also been added. This comparison was made b}^ means of a 

 colori me ter. The tube containing the distillate was allowed to 

 stand on a glass piate, and dose by it a similar but graduated tube, 

 in which, by means of a tubulure near the bottoni, the height of the 



1 Water Analysis. lOf' Ed. pag. 33. 



