570 



CKESSWELL SHEARER. 



with the coelomesoblast (see Text-fig. 9, liid.) thiit one would 

 certainly be led to think that they formed part of these bands, 

 unless their cytogeny had been carefully followed" (p. 223). 

 They have been described as follows in Podarke by Tread- 

 well (43). They arise as in TimlasseJua from the 3(l,3c, 

 :ind -Ui, and sink into the segmentation-cavity, where they 

 arrange themselves symmetrically, forming bands of three or 



Text-fig. -Jo. 



oes. 



Stmc-i- 



.._^— Kk. 



Ol iliqne corneal section tlirongh early trocliopliore of E ii ] i u m ;i t n s. 

 Ijetterins^ as in fig. 'I'l. 



more cells. " Since the posterior end of each band lies very 

 close to the definitive mesoblast, the effect is that of a well- 

 developed mesoblast band, lying iu the usual position in the 

 segmentation-cavity" (p. 427). 



The median portion of the ectomesoblast in iMipomatns 

 retains its position untransformed into larval musculature 

 until a very late stage, when the trocliopliore bi'comes seg- 

 mented. It is shown under the apical organ of the early 

 trocliopliore in figs. 9, lU, 16 {mesc). In the fully formed 

 trocliopliore it is shown in figs. 2, -3, and (3 {uicac.). 



