424 Dr. E. S. Morse on the Earl?/ Stages 



shell are no longer ];)arallel, though the hinge-margin has 

 nearly the same outline as in the first stago. 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 witli the FoJijzon. — The general affinities of the 

 BrachiojDoda with the Polyzoa, as indicated Ly ^lilne-Edwards, 

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

 by most zoologists. 



In the preceding examinations of the early stages of Tere- 

 hratuUna we have additional evidence of their relationship. 

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

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

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

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

 phore of the su])erior or Phylactoljematous Polyzoa. The 

 brachial fold, a delicate membrane bordering the loj)hophore, 

 immediately within which the cirri spring, as seen in Lingula 

 and Dlscina, may properly be compared to the calice in the 

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

 bordering the mouth, very pliant and active, maybe compared 

 as to function and ])osition to the epistome of the Polyzoa, 

 though not occu])ying 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- 

 (Ucella there are two flexible cords connecting the stomach 

 and the endocyst, called by Allman the anterior and posterior 

 funiculus, to Avliich arc attached respectively the ovary and 

 testis. In Liugida and Discina we find the reproductive 

 organs attached to bauds that connect the stomach and intes- 

 tine to the perivisceral wall. In Alcyonella the ovaiy arises 

 from the endocyst ; and likewise in TerehratuUna and allied 

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

 tive organs. 



The early appearance of the divaricator muscles in Tcre- 

 hratuJiiHi W(nild justify Mr. Hyatt in his views that these 

 muscles repicsent the retractors of the Polyzoa*. 



The combination of the stomach and intestine in their early 

 stages, Avith 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 Miiller has noted in an earlv stage of 



A. Hyatt, "Observations on Polyzoa, suborder rhvlactola?mata," 

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



