TliOCHOl'HOIlE OF HYDEOIDES UNCINATUS (ErPOMATCS). 581 



these, again, iti turn divide equally. One cell remains attached 

 to the gut-wall, as shown in a late stage in fig. 17 {jini-), 

 but this cell does not divide in this stage, and the growing 

 point of the bands is not here, but towards the ends nearest 

 the oeosphagus. The position of this cell alone gives it the 

 appeai-ance of being a pole-cell. 



According to A\^ilson (48) there is a complete absence of 

 teloblastic growth in the species of Hydroides studied by 

 him, for he states : " I have carefully studied the develop- 

 ment of Hydroides dianthus (a form nearly allied to 

 Eupomatus) by following the cleavage of the living ovum, 

 by examination of stained and cleared embryos, and actual 

 sections. The cleavage is in every detail identical with that 

 of Eupomatus, the gastrulation takes place in essentially 

 the same manner, and the trochophore is of quite the same 

 type. Yet I have been unable to identify the teloblasts at 

 any period. They are certainly not present at a stage when 

 the mesoblast bands consist of not more than four or five 

 cells each. At this period each band ends posteriorly in a 

 group of about three cells, two of which are not perceptibly 

 larger than the others, are joined by a narrow bridge of 

 protoplasm stretching across in the angle between the procto- 

 dajum and the wall of the anal vesicle" (p. 215). 



In Thalassema, Torrey (41) has not been able to find a 

 teloblastic growth of the bands. "It is a fact," he says, "as 

 far as 1 know, without exception, that in all forms where 

 there is a trochophore stage of long duration (as in the case 

 of all Annelids with equal cleavage), the two coelomesoblast 

 cells do not, in the earlier stages at least, bud like teloblasts" 

 (p. 222). 



As the bands grow out from the gut-wall in Eupomatus, 

 they keep quite apart from the mesenchyme cells of the 

 blastocoel, nor have I been able in any of the stages I have 

 studied to observe the origin of these cells from the ends 

 of the bands. Tliis is a very debated point in Annelid 

 embryology. Are not the numerous mesenchyme cells of the 

 blastocoel in part derived from the ends of the bands? So 



