_ 9 — 



most places consists of a single layer of cells, tt does 

 not as yet extend over the entire surface of the embryo, 

 patches on the sides of the abdomea being still void of 

 this covering. 



(2) The C 03 lorn. — I have not been able to follow 

 out the development of the coelom. In my younger 

 embryos it was, of course, not to be found. At this stage 

 it has already reached a high development. I consider 

 two layers of cells found under the epidermis, which send 

 folds into the interior of the yolk, to be the coelom, from 

 their resemblance to the coelom of Spiders and Scorpions. 

 The coelom also enters the bases of the legs. With the 

 folds the Anlagen of the future dorso- ventral muscles of 

 the cephalothorax and abdomen also enter the yolk. 

 Between ccelom aud epidermis are also found the first 

 Anlage of the segmental muscles, which arise from the 

 somatic ccelom layer. 



(3) The Lateral Organ. — The lateral organ of 

 the Pedipalps has already been described by Laurie (31) 

 and Strubell (42); it has also been described by Bruce 

 (9) and Pereyaslawzewa (37). 



In the stage which we are now considering the 

 lateral organ seems to be at the height of its development. 

 It appears as a horseshoe-shaped excrescence on the 

 base of the coxa of the fourth extremity, which it covers 

 on both sides. It is always covered by shreds of some 

 dark substance, 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 that 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) 



