NORTH AMF.IIICAN EARLY TERTIARY BRYOZOA. 811 



FIG. 267. Family Lichenoporidae Smitt, I860. 



A. Embryo of Lichenopora at the time of the division of the ectoderm into two distinct halves 

 of which one is destined to be recovered. 



B. Embryo of Lichenoporu liispida Fleming, 1828. Meridian section of an embryo more ad- 

 vanced in its development than the preceding one. The internal sac (si) the corouua (co) the 

 thickness of the calotte (cal) and the palleal epithelum (c) are differentiated at the cost of the 

 external cellular layer. The internal cellular layer forms a lining which continues to the cavity 

 of the embryo. (After Calvet, 1900.) 



C. Larva of Lii-ln'iinpitrn ; it is flat and not elongated as in the other Cyclostomata ( *, in- 

 ternal sac). The calotte is covered by the mantle, a feature which does not exist in the larva of 

 the Cheilostomata. (After Barrois, 1886.) 



D. E. Protoecium of Liclicitopnrtt seen from the front and in profile. (After Barrois, 1886.) 

 F-R. Lichenopora i-crnicnsa Fabricius. F-I. Drawings showing development of the ances- 



trula and formation of the zoarium. 



J. Colony in which the roof of the ovicell -is developing. The aperture of the ovicell is not 

 yet completely formed. The proximal edge of the basal lamina has nearly reached the protoe- 

 cium. 



K. Part of the growing edge of an adult colony, showing the way in which new zooecia are 

 formed and representing various stages in the development of the alveoli. 



L. Horizontal section of a colony consisting of three complete zooecia only and showing the 

 anatomical structure. 



M. Thick radial section of part of an old colony showing the relations of the ovicell to the 

 zooecia. 



N. Diagram of the growth of the margin of the colony. The thick lines represent two young 

 zooecia and part of the basal lamina as they would be seen in the radial section, and the dotted 

 lines represent the condition of the corresponding parts after a certain amount of growth has 

 taken place ; ACHB is the basal lamina. The zooecium whose point is marked D has its upper 

 end free, even in the earlier condition, while that marked E is still incomplete on its distal side 



(fig. K). 



O. Entire colony stained and mounted in Canada balsam. The shaded part shows how- 

 much of the ovicell is completely roofed. The alveoli which are still unroofed are not specially 

 indicated. The ovieell has an aperture, at the base of wfiich is the fertile brown body (primary 

 embryo). Parts of the zooecia which are seen either through other zooecia or through-the roof 

 of the ovicell are indicated by dotted lines. The colony is left-handed. Z2 is occluded and was 

 obviously fertile and would hardly have been visible at all in a dry preparation. The embryo- 

 phore is that part of the ovicell in which the secondary embryos are developed. 



P. Zooecia from an old colony. The alveoli are still distinctly visible and the cancelli are 

 commencing in the interalveolar grooves or at the base of the zooecia. The left hand zooecium is 

 closed by a porous calcareous cap. 



Q. Two zooecia from a very old colony, with secondary thickening. The porous roof of the 

 ovicell is seen at the bottom of a set of honey comb-like spaces, the so-called " cancelli " ; some of 

 these are covering the bases of the zooecia, and in the left hand zooecium these are entirely or 

 partially roofed. Two of the blister-like swellings thus formed have part of their roof still un- 

 calcified. 



R. Diagram to explain the difference between "right-handed" (dextral) and "left-handed" 

 (sinistral) colonies. (F-R, after Harmer, 1896.) 



