50 



BRYOZOA ECTOPROCTA. 



The statoblasts arise in connection with a mesodermal strand 

 known as the funiculus, which runs from the end of the stomach- 

 caecum to the zooecial wall (Fig. 28, /). Along this strand they 

 are arranged in a chain, the youngest visible rudiment of a stato- 

 blast appearing at the end of the funiculus nearest to the zooecial 

 wall, while the most developed are found near the stomach -caecum. 



To obtain a clear view of the origin and significance of the stato- 

 blasts, we must, following Braem, examine the earliest stages in 



the development of the 

 funiculus. This strand 

 first arises as a fold-like 

 prominence in the outer 

 (mesodermal) layer on 

 the oral side of the neck 

 in the young polypide- 

 rudiment. In the fur- 

 ther course of develop- 

 ment, this fold separates 

 from the neck of the 

 polypide-rudiment (Fig. 

 25 A), so that it as- 

 sumes the form of a 

 short strand (/), this 

 beins; inserted at its 

 upper end into the 

 zooecial wall, and at its 

 lower into the j^olypide- 

 rudiment. Through the 

 further growth of the 

 zooecial wall, the upper 

 point of insertion of the 

 funiculus shifts further 

 and further from the 

 aperture of the polypide, 

 and may finally reach 

 the basal surface of tlie 



Fio. 25.— A, young polypide-bud of Plumatella with the 

 rudiment of the funiculus (/) (after Braem). x, inner 

 (ectodermal), y, outer (mesodermal) budding layer. B, 

 longitudinal section through a funiculus of Cristatella 

 {after Braem). hm, "formative mass"; eg, "cystigen 

 part" of the statobla-st rudiment (st) ; e, ectoderm ; ec, 

 inner (ectodermal) layer of the funiculus ; m, outer 

 (mesodermal) layer of the funiculus. 



zooecium. 

 The funiculus, in its origin, is, as we have seen, purely meso- 

 dermal. Very soon, however, a conical mass of ectoderm-cells, 

 capable of further growth by division (Fig. 25 B, ec), grows out 

 from the zooecial wall into the funiculus, which in this way becomes 



