Genera of the ]N'okth American Palaeozoic Bryozoa. 465 



In ^, the lophophore has lost its crescentic shape and become 

 orbicular ; the different portions of the animal are well defined. 

 Hitherto there has been no external opening in the cell, and the 

 nourishment has been effected from the parent cell; but now an 

 opening occurs at the extremity of the young cell ; the different 

 organs rapidly become perfected, and the polyp is capable of 

 obtaining nourishment from without. 



Fig. 29 represents the development of a free embryo of Alcy- 

 onellafungosa; a represents the free spermatozoa greatly enlarged; 

 h a group of ova; c a single ovum much more enlarged. In d the 

 ovum has undergone segmentation and a central cavity has 

 begun to show itself. Fig. e represeitts the ovum developed into 

 an oval ciliated sac destitute of an external opening. In/" the 

 embryo presents an orifice, through which an unciliated portion 

 is protruded by a process of evagination; in this protruded portion 

 a polyp is developed. Fig. g shows the polyp isolated from 

 the cell, and further enlarged ; the lophophore is yet destitute 

 of tentacles. Fig. h shows the polyp more advanced ; a few of 

 the tentacles have begun to develop on the lophophore. Fig. i 

 shows an embr3^o containing two polj^pes ; fig. k the same more 

 advanced, the pol3^ps having acquired nearly their perfect 

 development. Fig. I shows a more advanced stage. The first 

 invagination has become obliterated ; the cilia have disappeared 

 from the surface, and the young Bryozoan has acquired its ecto- 

 cystal investment. A new bud is seen at each side within its 

 cell, near its anterior extremity. 



For the knowledge of the development of Phalangella fldbel- 

 laria, a gymnolaematous bryozoan of the sub-order Cyclostomata, 

 I am indebted to Jules Barrois' " Embryologies de Bryozoaires," 

 from which work I have copied the figures on Plates C, D and 

 E. The first stage recognized is that of a morula already well 

 formed and composed of numerous, comparatively large, vitelline 

 spheres (Plate C, fig. 3). The morula does not yet show any trace 

 of a central cavity, and is very easily seen to be composed of a 

 great number of the round cells represented in figs. 1, 2. 



In the following stage the morula is slightly enlarged, and the 

 vitelline spheres are segmented into more and more numerous 

 elements. 



59 



