60 



Guide to the Invertelrata. 



Bryozoa. 



GALLERY 

 VIII. 



Centre- 

 cases 



86a & 86b, 

 Wall-case 

 12a. 



Bryozoa are frequently found upon the seashore, either spreading 

 in delicate gauze-like sheets over weeds, shells, and stones, rising 

 in hard shrub - like tufts, forming hemispherical masses, or 

 spreading in flexible horny branches. Owing to their mode of 

 growth, they are generally mistaken for seaweeds. The classifi- 

 cation of the Bryozoa depends upon the structure of the small 

 "zooids," and the microscope is indispensable in their study. 

 In the arrangement of the collection, therefore, specimens are 

 exhibited to show the general form and "habit" of the colony, 

 and drawings are placed beside them to show the minute structure 

 of the zooids. The specimens are in most cases sufficiently near 



Tm 



Fig. 103. — Diagram of structure of a typical Bryozoan zooid. an. anus; 

 ap. aperture ; b.c. body-cavity ; c.p. communication pore ; d. diaphragm ; 

 ect. ectoderm ; end. endoderm ; /. funicidi ; n. nerve-ganglion ; o. orifice ; 

 oes. oesophagus ; op. operculum ; r.m. retractor muscle ; st. stomach ; 

 T. tentacles ; t.s tentacle sheath. 



Wall case 

 12a. 



to the front of the case to admit of the use of a magnifying glass, 

 and thus the main features of the zooids can be recognized. Some 

 of the colonies too large to be included in the table- cases are 

 placed in Wall-case 12a. 



Most of the living Bryozoa are soft-bodied animals, and only 

 two, or possibly three, of the existing orders are represented in 

 the fossil faunas. There are two other orders (the Trepostomata 

 and Cryptostomata), which are now extinct. The fossils, however, 

 all belong to the Gymnolaemata, one of the three main divisions 

 of the Bryozoa. 



The Bryozoa are abundant fossils in many formations, and 



