THÉEL, THE AMOEBOCYTES BY ECHINODERMS. 29 



bodies in question is to be found in other holothurids, too, 

 for inst., in Thyone fusus and Stichopus tremula but there they 

 evidently are in want of a nucleus, and may be looked upon 

 as löst elements of tissues. 



Cucumaria lactea. 



The crystals present themselves under two different types : 

 rhombs or rhomboids and digitiferous crystals, the latter being 

 a provisional name given on account of their extreme appear- 

 ance, pro vid ed, as they are, with a number of digitiform 

 processes. 



The rhombs or rhomboids are common in most of the holo- 

 thurids examined by me, and they often occur in company 

 with other forms of crystals. They reach a length of from 

 22 [1. to 27,8 \L and fill up the mother-cell. In fresh state, they 

 shine whitish and often they show four refracting granules 

 arranged in such a manner that they form a small rhomb 

 inside the true one, presuming them to be j oined by lines (pl. 

 3, fig. 11). Not seldom rhombs are met with which have the 

 acute angles truncated, the stumped ends forming either 

 straight lines or inwardly turned obtuse angles (pl. 3, figs. 13 

 and 14). 



Among those rhomboids other forms occur which are 

 smaller and seem to be in a state of growth, from 11,4 \l to 

 15,2 [JL in length. A careful examination of them reveals that 

 we have to do with crystals of somewhat various appearance. 

 One of them is biconvex, lenticular in side-view — ef. text-figure 

 7: 2 and 4. Another has the two opposite surfaces parallel A\ith 

 the sides or edges thick and straight, while a third one has 

 the thick edges concaved — ef. text-figure 7: i, 3, 6, 7. The 

 mother-cells themselves of these smaller rhomboids are spher- 

 ical and show not seldom a set of light vacuoles — ef. text-figure 

 7: 1, 2, 5. In some instances the globular mother-cells contain 

 several small, refracting crystals which may eventually be dis- 

 solved in order to give rise to a true rhomboid — ef. text- 

 figure 7: 5. 



The second type of crystals is represented by characteristic 

 bodies particular to the species in question and to which I 

 proposed the name »digitiferous crystals». A giance at the 

 figures on plate 3 and at those in the text will give the best 

 idea of their peculiar shape. Their refraction is less brillant 



