570 E. W. MACBEIDE. 



it Avill be noticed that the culture obtaiued by natural 

 fertilisation in 1905 developed at a quicker rate tlian tliat 

 indicated by tliese figures. 



The larva3 were observed and drawn living. Those pre- 

 served in osmic acid and MuUer's fluid were sectioned. For 

 this purpose the celloidin paraffin method was used, and the 

 procedure adopted was similar to that employed in the case 

 of Echinus esculent us and described in my paper on the 

 subject (19). One additional caution, which it was found 

 necessary to adopt, may be mentioned here. It transpired 

 that if the sections, after being spread out on hot water in 

 order to flatten them, were left to dry for longer than forty 

 minutes on the top of the thermostat, great cracks developed 

 in them OAving to the shrinkage of the celloidin. 



When it was necessary to supplement the information 

 obtained from views of the living hxrva3 by whole mounts of 

 preserved ones, these were cleared from osmic acid. This 

 was done by placing them in water or weak alcohol. The 

 vessel containing them was then placed (open) inside a larger 

 vessel on the bottom of which was a layer of crystals of 

 chlorate of potash on which strong hydrochloric acid was 

 poured. The larger vessel was closed. The euchlorine gas 

 evolved became dissolved in the fluid of the smaller vessel 

 and oxidised the black deposit of metallic osmium in the tissues. 



In the orientation of sections the postero-lateral arms of 

 the larva Avere of the greatest assistance, for they persist 

 until the metamorphosis is quite complete, so that they mark a 

 constant plane amidst the varying position of the other organs. 

 This plane will be called the frontal plane, and most of the 

 sections were cut parallel to it. Sections parallel to the 

 median sagittal ])lane of the larva were also employed as 

 were transverse sections when they became necessary in 

 order to elucidate special points. 



Normal and Abnormal Development. 

 It has already been mentioned that eggs fertilised under 

 different conditions give rise to larvic which in their early 



