XI 



PHYLUM ARTHROPODA 



565 



segments the division beginning in front. The lips of the blasto- 

 pore meanwhile become approximated, and fuse throughout the 

 greater part of their length, leaving only an anterior and a 

 posterior opening; these go to form the mouth and the anus 



FIG 



. stage 



is closing up in its middle part ; (.', stage in which the blastopore has become >!. ,*rd up except 

 the anterior part which has gone to form the mouth (mo.), and the anus ('</<.); the whole embryo 

 has now become strongly curved towards the dorsal side. (After Bo If our.) 



respectively. The division into segments soon becomes well 

 marked. At the anterior end the head lobes become distinguish- 

 able. The body elongates, and the head and trunk become differ- 

 entiated. The limbs now arise as ventro-lateral outgrowths which 

 are developed from before backwards. 



