424 Dr. E. S. Morse on the Early Stages 



shell are no longer parallel, tliongh the hinge-margin has 

 nearly the same outline as in the first stage. In the adult 

 shell the outline assumes entirely different proportions, being 

 nearly oval, while the hinge-margin forms a sharp angle, and 

 the foramen is quite circular. 



Relations with the Polyzoa. — The general affinities of the 

 Brachiopoda with the Polyzoa, as indicated by Milne-Edwards, 

 Huxley, Hancock, Agassiz, Hyatt, and others, are admitted 

 by most zoologists. 



In the preceding examinations of the early stages of Tere- 

 hratulina we have additional evidence of their relationship. 

 In the evolution of the lophophore, from its circular character, 

 surmounted by a few cirri, to that of the hippocrepidan stage, 

 we have suggested, first, the circular lophophore in the inferior 

 or Gymnolffimatous Polyzoa, and, finally, the bilateral lopho- 

 phore of the superior or Phylactolffimatous Polyzoa. The 

 brachial fold, *a delicate membrane bordering the lophophore, 

 immediately within which the cirri spring, as seen in Lingula 

 and Disciiia.) may properly be compared tb the calice in the 

 higher Polyzoa. Still later, the presence of a distinct fold 

 bordering the mouth, very pliant and active, may be compared 

 as to function and position to the epistome of the Polyzoa, 

 though not occupying a homological position with regard to 

 flexure of intestine. It would appear that the membranes 

 suspending the stomach and intestine in the perivisceral cavity 

 have some relation to the funiculus in the Polyzoa. In Palu- 

 dicella there are two flexible cords connecting the stomach 

 and the endocyst, called by Allman the anterior and posterior 

 funiculus, to which are attached respectively the ovary and 

 testis. In Lingula and Discina we find the reproductive 

 organs attached to bands that connect the stomach and intes- 

 tine to the perivisceral wall. In Alcyonella the ovary arises 

 from the endocyst ; and likewise in Terehratulina and allied 

 genera we find the mantle, or endocyst, holding the reproduc- 

 tive organs.' 



The early appearance of the divaricator muscles in Tere- 

 hratulina would justify Mr. Hyatt in his views that these 

 muscles represent the retractors of the Polyzoa*. 



The combination of the stomach and intestine in their early 

 stages, with the presence of hepatic cells lining their inner 

 walls, and the presence also of a cardiac valve or constriction, 

 all recall similar parts in the higher Polyzoa. 



That these relations may be carried further there is no 

 reason to doubt. Fritz Mtiller has noted in an early stage of 



* A. Hyatt, " Observations on Polyzoa, suborder Phylactolsemata," 

 Proc. Essex Instit. vols. iv. & v. Salem, Mass, 



