— 10 — 



are deeply stained with eosin ; they protrude into the pro- 

 cesses of the cuticle, at whose bases a dark substance is 

 being deposited. The nuclei of these cells are obloDg, 

 and take a deep stain from hematoxylin. 



The internal wall of cells resembles the external in 

 its histological elements, with the difference that its cell 

 walls are not visible, and that the cells have no distinct 

 outline, so that it is almost impossible to determine their 

 boundaries. On the side of this wall nearest to the body 

 of the embryo protoplasmic processes of these cells are 

 seen enveloping yolk particles. 



The yolk in the one cavity does not resemble that in 

 the other. In the outer cavity, enclosed by the external 

 and internal wall, this yolk consists of very minute 

 particles, which appear to have had to pass the internal 

 wall before having reached the external cavity. The yolk 

 in the internal cavity still in every respect resembles that 

 filling the abdomen, and is in direct communication with it. 



At the base of the lateral organ, where it is attached 

 to the base of the fourth extremity, the epidermis has 

 begun to grow inwards, forming a partition between the 

 lateral organ and the leg. This partition has still an 

 opening in the middle, through which the inner cavity 

 of the lateral organ communicates with the yolk of the 

 embryo. Later on this opening closes, after which the 

 lateral organ becomes functionless and drops off. 



The lateral organ of the Thelyphonidse has been 

 described by Strubell (41), and there is no doubt that it 

 is identical with that of Ad met us. Tn other orders of 

 Arachnids we only find the lateral organ in Solpugids 

 and Pseudoscorpions. 



Croneberg (10) described the lateral organ of Gale- 

 odes. This also seems to be very similar to that of 

 Admetus. I have also been able to find a similar 

 organ in a young adult Chelifer ; it seems to me to 

 have already become functionless, and much resembles that 

 described for Admetus in the fifth stage. The possession 

 of a lateral organ seems to me to point out a nearer re- 

 lationship between these three groups. 



