52 



BRYOZOA ECTOPROCTA. 



cells now form the annular float, the whole surface of each of 

 them becoming cuticularised. The protoplasmic body remaining 

 within the cuticular cells then completely disappears. When the 

 annular float is completed, it is grown over from above and below 

 by the margins of the central caps of the chitinous secreting layer, 

 which then secretes an external enveloping chitinous layer (Fig. 27, 

 ud and od). 



In Cristatdla, the equator of the developing statoblasts is at right angles to- 

 the longitudinal axis of the funiculus. In Plumatellct, on the contrary, it lies- 

 parallel to that structure. The elongated form of the statoblasts of Plumatella 

 is explained in this way. The most complicated conditions are found in the 

 annular float of Cristatella. For an account of these \ve must refer the reader 

 to VERWORN and BRAEM. 



R 



FIG. 26. Three ontogenetic stages of the statoblasts of Cristatella (after VERWORN). a, cysti- 

 gen half; a', external layer; a", inner layer of the cystigen half; &, formative mass;, 

 c, cuticular envelope ; p, point where during circumcrescence a pore forms ; /, funiculus. 



The germ -body proper consists of the ectodermal layer (Fig. 

 26 C, a") and of the formative mass (l>) which this surrounds. In 

 proportion as the cells of the latter become filled with food-yolk 

 the boundaries between them disappear. But not all the cells of 

 the formative mass undergo this transformation. Some of them 

 which are in close contact with the ectodermal layer remain 

 unchanged. It appears that these cells, which BRAEM found to be 

 specially plentiful in Cristatella, where they often form a continuous. 



