THE DEVELOPMENT Oi' ADMETUS PUMILIO. 603 



pair making an exception, the tibia and tarsus of which run 

 along the under side o£ the other legs. 



The whole embryo is enclosed in a loose outer skin, which 

 follows the contour of the whole body, extremities included, 

 without ever actually touching it, except, perhaps, in the 

 region of the lateral organ, and in parts of the dorsal side of 

 the abdomen. This cuticle is covered in parts with numerous 

 wart-like processes, as mentioned by Pereyaslawzewa (37) 

 and Laurie (31). On surface views nothing further is to be 

 seen ; we will therefore proceed to the descriptiovx of the 

 organs as seen in cuts. 



(1) The Skins. — The outer cuticle just mentioned is seen 

 in cuts to consist of several exceedingly thin strata ; it is 

 otherwise perfectly structureless. The embryo itself is 

 covered by a thin epidermis, which in most places consists 

 of a single layer of cells. It does not as yet extend over 

 the eutire surface of the embryo, patches on the sides of the 

 abdomen being still void of this covering. 



(2) The Coelom. — 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 and epidermis are also 

 found the first Anlagen of the segmental muscles, which arise 

 from the somatic coelom layer. 



(8) 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 



