of Terebratulina septentrionalis. 421 



recalls the hippocrepldan forms among the Polyzoa, such as 

 Plumatella^ Cristatella, Lophopus^ and others. 



The liver now shows its adult characters in having its 

 ramified c^ca separated and not adhering by their walls in 

 one mass. In this early condition it resembles the liver of 

 Thecidiumj as described and figured by Lacaze-Duthiers. 



Fig. 18 represents a stage where the arms become deflected; 

 as yet no central process of the lophophore is developed ; the 

 mouth is very large, and that margin of it not bearing cirri is 

 very pliant in its movements. 



In the next stage (fig. 19) the arms are more deflected and 

 make a sharper curve in their approach together, and the 

 central process of the lophopore is indicated by that portion 

 forming the base of the inner curve developing into two pro- 

 minences. The free lip is seen in irregular curves, and these 

 changed with every movement of the parts. 



Fig. 20 represents a slightly more advanced stage, where 

 the central processes of the lophophore are more developed. 

 The free lip is here seen thrown broadly back, disclosing a 

 capacious mouth, within which are seen two blunt projec- 

 tions, though in another view of the mouth only one pro- 

 jection was observed. The free lip seemed to perform all the 

 functions pertaining to the epistome in the higher Polyzoa ; 

 and we find it on the inner bend of the arms, as in the Polyzoa, 

 though not occupying the same homological position with 

 regard to the flexure of the intestine. It will be noticed that 

 in all these stages the cirri are comparatively thick. 



In the stage represented by fig. 21, the cirri become more 

 attenuated and increase rapidly in number ; the central pro- 

 cess is more advanced, though not yet thrown into a vertical 

 spiral, as in the adult ; and the mouth has lost the broad re- 

 flected character of the lip which it possessed in the earlier 

 stages, though the free lip has yet considerable pliancy. 

 For the first time now appears another adult character, in the 

 apparent decrease in the length of those cirri in the median 

 line of the mouth. 



In fig. 22 the mouth of an adult individual is shown, with 

 the cirri. In this view the oral tubercle (o^), as it may be called, 

 is strongly marked. The same projection is represented in 

 the mouth of ThecicUum mediterraneum as figured by Lacaze- 

 Duthiers. A singular lunate groove, running parallel with 

 the free lip, is indicated in the figure, which ma}^ be called 

 the oral groove {og). It seems more like a wrinkle caused by 

 the expansion of the free lip, though its limits are well defined 

 and the furrow is quite deep. 



The independent movements of the cirri are shown in 

 Ann. & Mag. N. Hist. Ser. 4. Vol. viii. 32 



