Genera of the E'oeth American Palaeozoic Bryozoa. 473 



In Plate E, figs. 1, 2, show the free embryo, front and back 

 view of MoLLiA. 



a, Ciliary plume, h, Mouth of gastrula. c, Oculiform points. 

 d^ Obscure portion of the body, comprised between the two . 

 branches of the stomach (intestine of Kepiachoff?). 



Figures 3 and 4 show the changes toward the formation of a 

 cell. j9, The polyp. /, Fatty globules disseminated in the period 

 following fixation, e, Endocyst. e', Ectocyst. s, The peri- 

 pheral zone. In fig. 5 the calcareous ectocyst has acquired its 

 normal thickness, while the peripheral zone has disappeared, as 

 we have already seen in Tdbulipora. The primitive cell is now 

 completely formed and has always on the right or left a lateral 

 cell. Figure 6 represents a more advanced stage than fig. 

 6. The lateral cell 1, after increasing in size, buds and is now 

 divided by a wall into two superimposed cells, 1 and 1', both 

 stiU incomplete. In fig. T the cell 1 has acquired its com- 

 plete development, but has not given birth to another cell. The 

 cell 1', has increased in size and shows two new cells, 2 and 2', 

 budding from it, showing in this stage as two lateral swellings ; 

 2' is already divided from its parent cell by a wall. In ^g. 8 we 

 see that the rudimentary cells of the preceding figures have in- 

 creased in growth, V being completely formed and the others 

 well advanced ; moreover, we see that the cells 1, 2, 1' and 2^ are 

 spread out to the left in such a manner as to fill the space be- 

 tween them and the neighboring cells, a process resulting in 

 three new cells, 3, 3' and 3". In fig. 9 we see that the cells num- 

 bered 3 have increased in size, while the cells numbered 2 are • 

 nearly or quite completed, whilst the cells numbered 3 have 

 spread out in such a manner as to fill the interstices between 

 them and the cells \\ 2, 2', giving birth to a new range of cells 

 numbered 4, composed of more and more numerically, which in 

 turn thicken and give birth to another range. This form of 

 growth continues indefinitely, each range of rudimentary cells 

 giving birth to a new range, while the cells of the preceding 

 range acquire their complete character. The continuation of 

 this mode of growth finally forms a discoidal muss, the primitive 

 60 



