194 



ZOOLOGY. 



authors), or away from the perpendicular end (D), and is 

 surrounded by a few ciliated cirri, which forcibly recall cer- 

 tain Polyzoa. The stomach and intestine form a simple 

 chamber, alternating in their contractions and forcing the 

 particles of food from one portion to the other." Figure 

 133, E, shows a more advanced stage, in which a fold is 

 seen on each side of the stomach ; from the fold is developed 

 the complicated liver of the adult, as seen in E, which 

 represents the animal about an eighth of an inch long. The 

 arms (lophophore) begin to assume the horseshoe-shaped 

 form of Pedinatella and other fresh-water Polyzoa. At this 

 stage the mouth begins to turn towai'ds the dorsal valve, and 

 as the central lobes of the lophophore begin to develop, the 

 lateral arms are deflected as in F. . In the stage G an epis- 

 tome is marked, and Morse noticed that the end of the 



Fig. 133. — Later larval stages of Terebratulina-^After Morse. 



intestine was held to the mantle by an attachment, as in the 

 adult, reminding one of the fioniculus in the fresh-water 

 Polyzoa. In tracing the development of Argiope, Kowal- 

 evsky has shown that the larva is strikingly like those of the 

 Annelids, as well as the Tornaria stage of Balatwglossus. 



While in their development the BracMopoda recall the 

 larvEe of the true worms, they resemble the adult worms in 

 the general arrangement of the arms and viscera, though 

 tliey lack the highly developed nervous system of tlic Anne- 

 lids, as well as a vascular system, while the body is not 

 jointed. On the other hand they are closely related to the 

 Polyzoa, and it seems probable that the Brachiopods and 

 Polyzoa were derived from common low vermian ancestors, 

 while the true Annelids probably sprang independently 

 from a higher ancestry. They are also a generalized type. 



