— 22 — 



9. The Muscles. — Typical muscles are as yet 

 nowhere to be found. In the extremities, and also in 

 the abdomen, we find the cells which give rise to the 

 future muscles. These are distinguishable by their long, 

 granular nuclei. Though already spindle-shaped, they do 

 not as yet stain with eosine, as the muscles in more 

 advanced embryos always do. 



10. The Genital Organs. — The genital organs 

 have not as yet begun to make their appearance. 



Stage V. 



The two illustrations (figs. 1 and la) of the embryo 

 at this stage will give a very good idea of the general 

 superficial appearance of these embryos. They appear in 

 almost every respect similar to the embryos of the fourth 

 stage, and the description of those embryos only requires 

 a few additions to be perfect for the embryo of the fifth 

 stage. 



In the first place we must remark the median eyes. 

 They are now very deeply pigmented, except in a narrow 

 line which separated the two eyes. 



The lateral eyes are now also visible; they resemble 

 Y-shaped marks on both sides of the median eyes. This 

 is caused by the pigment being deposited between the 

 single ocelli, wliich are three in number. The margin of 

 the fold carrying the median eyes is also more distinctly 

 visible than in the fourth stage. 



1. The Skins. — No important change can be 

 observed in the skins since Stage IV. 



2. The Ccelom. — The coeloin has undergone many 

 changes since Stage IV. It has, for instance, given rise 

 to the muscles, of which at least two sets are to be 

 distinguished. A dorso-ventral muscular system has 

 followed the foldings of the caelum, and* now * consists of 

 a paired muscle in each segment, running from the 

 carapace to the ventral side, except perhaps in the first 

 two segments of the cephalo-thorax. The other set 

 consists of the inter-segmental muscles. These run parallel 

 to the surface, from segment to segment. The walls of 



