ON THE ORIGIN OP VERTEBRATES FROM ARACHNIDS. 371 



In Cyraothoa the multiplication of the teloblasts goes 

 on with great regularity (Fig. 17). This condition is un- 

 doubtedly a mere modification of that found in most insects. 

 But it is incredible that these teloblasts can have anything to 

 do with a gastrula. There is no segmentation of a continuous 







Fig. 17. — Formation of layers iu Cymothoa. — A. Median longitudinal 

 section of posterior end of germ band. B. Posterior end of embryo, 

 seen from below ; the rows of inner layer cells are not represented on 

 the right. The last row of ectodermic teloblasts often divides simul- 

 taneously along its whole length. 



sheet of mesoderm, but each somite arises from the repeated 

 division of a single row of eight cells. Each somite consists of 

 two lateral parts arising from the six lateral mesoblasts, and a 

 median one arising from the two median mesoblasts. 



I long ago pointed out that in Phryganids the neural furrow 

 is developed in the anterior portion of the germ band before 

 the terminal pore has disappeared, and that its posterior end 

 extends into the terminal pore. I then stated, and still main- 

 tain, that an incipient neureutric canal is thus formed, 

 similar to that in Vertebrates. 



