74 



NATURAL HISTORY. 



Now. in the then existing scheme of classification, the brachiopods were 

 included in the molluscs from the simple reason that they had a bivalve 

 calcareous shell, while all the differences between the animals were ignored. 

 These brachiopods, for instance, had two long tentaculated arms near the 

 mouth, and from this as a basis the moss-animals were associated with 

 them, and were thus quickly transmogrified into molluscs. The next step 

 was a study of the brachiopods. It was shown that in internal structure 

 they bad nothing in common with the clams and oysters, and that even 

 the shell was very different. As we shall see, the shell of the clam consists 

 of two halves, on.- placed on the right, the other on the left side of the 



body ; but in the brachiopods, one 

 half was placed above the body, 

 the other below it. This study 

 of the internal structure revealed 

 several coincidences between the 

 brachiopods and worms, and hence 

 they were quickly declared to be 

 worms. The Polyzoa were of 

 course carried with them ; for 

 since their only claim to be con- 

 sidered molluscs rested on their 

 mblance to the brachiopods, the separation of these latter and their 

 union with the worms necessitated a similar course with the moss- 

 animals. The next step was a questioning of this vermian relationship, 

 a nd nexl of the relationship of the moss-animals and brachiopods to 

 each other. 



Brachiopods are to-day comparatively rare in the sea ; but such was 



nol the case in geological times, for in the older rocks they make up the 



il proportion of the fossils both in species and in specimens. On our 



whole easl coast to-day only three species are at all abundant. In short, 



the -roup of brachiopods is dying out. 



The moss-animals, on the other hand, are very numerous both in spe- 

 cies and specimens. Rocks, shells, and sea-weeds below low-water mark 

 reveal some of the forms forming a delicate lace-like network on the sur- 

 face, or like the species figured here, known as "Neptune's frill," forming 

 more substantial growths. This calcareous mass is not the product of one, 



If magnified, the surface shows innumerable little 

 cells 5 each occupied by a polyzoon, just like the polyps in a bit of coral. 

 The analogy goes farther, for these moss-animals increase like them by 

 budding, and each colony, no matter how large it be, is the result of a 

 single egg. 



Fig. 71. — A lirachiopod {Lingula). 



