604 L. H. GOUGH. 



the coxa of the fourth extremity, which it covers on both 

 sides. It is always covered by shreds of some dai'k sub- 

 stance, which is probably secreted by it. Cuts show that 

 the lateral organ is a more complicated structure than it 

 seems to me to have been considered as yet. 



I am not able to state anything as to the origin of this 

 structure, as I possess only embryos without the lateral 

 organ, or with it in later stages of development. 



Cuts show tluit the lateral organ consists of an outer layer 

 of cells, forming the external wall of the sac ; the interior of 

 the sac contains two cavities filled with yolk, which are 

 separated from each other by a second internal wall of cells, 

 running nearly parallel to the external wall. The cells 

 forming the outer wall of the lateral organ (fig. 5) are deeply 

 stained with eosin ; they protrude into the processes of the 

 cuticle, at whose bases a dark substance is being deposited. 

 The nuclei of these cells are oblong, and take a deep stain 

 from hgematoxylin. 



The internal walls of cells resemble 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 abdo- 

 men, 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 



