for laboratory study. After staining lightly in acid 

 carmine. so as to facilitate their orientation ,ths larvae 

 ?/ere dehydrated in the usual way and cleared in oil of 

 cloves . From the clove oil they were oriented by a mod- 

 ification or the PATTON method. After an impregnation 

 with 55° paraffin, series of setions three microns in 

 thickness were made in three planes , transverse (long- 

 itudinal sagittal and longitudinal horrisontal. The 

 sections were stained on the slide with KLEINENBERGS 

 haematoxylon. Other methods were tried but none proved 

 so satisfactory as the one just described. The shrink- 

 age in sehinoderm tissue, which usually accompanies the 

 unmodified paraffin method ^was not to be seen in the 

 tissues of thifese larvae due, no doubt, to their unusual 

 thickness. 



It has been thought best to make the following 

 list of terms which are used synonymously in the text 

 of this paper in the description of the larvae. Those 

 in the same line can, in most, cases , be interchangably 

 used. 



Dorsal , — aboral , — above , — over . 



Ventral , — oral , — below , — under . 



Anterior, — forward, — before. 



Posterior , — backward, — behind . 

 In the drawings of the larvae, when the ventral side is 



