Chap. 28 ANNELIDS PIONEERS IN SEGMENTATION 559 



pair (10) are pouches; the second and third pairs (11, 12) are glands (Fig. 

 28.7). The glands produce the chalky secretion, evidently from an excess of 

 calcium carbonate in the blood. From the glands it passes into the pouches, 

 trickling forward through channels created by the infolding of the lining of the 

 esophagus. The pouches act as storage sacs from which the secretion oozes 

 into the food mass as it passes by their openings. The function of the cal- 

 ciferous bodies has been variously interpreted. Their secretion has been said 

 to be a neutralizer that aids digestion. This was not borne out by the experi- 

 ments of J. D. Robertson who concluded that the calciferous organs eliminate 

 excess calcium that is absorbed from the food into the blood. The ways in 

 which animals have dealt with extra calcium has had far-reaching effects upon 

 them. Earthworms eliminate it and wriggle on with their soft, freely flexible 

 bodies unaffected. Snails and clams use it in protective shells with which they 

 are often weighed down in continual semicaptivity; vertebrates use it in their 

 bones. 



From the esophagus, food passes into the thin-walled and elastic crop, an 

 expansion of the esophagus (Fig. 28.6). It opens into a muscular gizzard with 

 a chitinous lining. This is essentially similar to the gizzards of grasshoppers 

 and chickens and performs the same work of squeezing and grinding. The re- 

 mainder of the food tube is the intestine where the main part of digestion and 



10 



II 



12 



Cavity of esophagus 



Esophageal pouch 

 Stored carbonaie 



Esophageal glands 



Wall of 

 esophagus 



Trough of 

 secretion 



14 



Fig. 28.7. Earthworms. Calciferous organs seen from the dorsal side. The glands, 

 11 and 12, absorb calcium from the blood and produce a chalky secretion that 

 trickles forward through the special channels in the lining of the esophagus visible 

 in a cross section. It passes into the pouches {10) where it is temporarily stored 

 before it oozes into the passing food masses. (After Robertson: "Calciferous 

 Glands of Earthworms," Brit. Jour. Exp. Biol, 13:279-297, 1936.) 



