44-2 



THE VOYAGE OF H.M.S. CHALLENGER. 



the comprehension of the plan of organisation and the structural relations, but they 

 were less applicable to the study of minute histological details, which undergo altera- 

 tion by treatment of the object with turpentine and embedding in paraffin. For this 

 purpose therefore other preparations were used, which were simply teased out or cut by 

 hand after being stained and then mounted in glycerin. 



Fio. 164. — Crnterotnorpha murrayi, n. «p., a representative of the Rossellida?. 



" The glycerin has the advantage over balsam not only in that the delicate outlines of 

 the cells may be more easily recognised, but also because, in consequence of its refractive 

 index agreeing very closely with that of the siliceous skeleton, this latter becomes almost 

 invisible, and thus the soft tissues stand out much more prominently. 





