THE BRITISH FOSSIL BRACHIOPODA. 307 



The researches also of Prof. E. Morse on the embryology of Terebratulina septentrionalis 

 have added new information. He states that the embryo presents a series of well- 

 defined stages, which he describes and illustrates with minute detail. " In the first 

 stage the embryo becomes expanded at one end ; the segments are barely indicated ; the 

 posterior end is the widest ; the anterior portion is ornamented with a conspicuous tuft 

 of long cilia, so peculiar to the embryos of many worms. The embryo is also clothed 

 with vibratile cilia, and in this condition slowly moves along the sea-bottom (one 

 placed in a dish did so). In the second well-marked stage the embryo is divided 

 into two prominent segments ; these expand and contract upon each other slightly, and 

 the cephalic segment has the power of partially bending from side to side. In this stage 

 the embryo is most active, swimming rapidly in every direction and turning abruptly 

 about. The oesophagus also becomes dimly defined. In the third stage the peduncular 

 segment is developed, and projects from the posterior portion of what can now be called 

 the thoracic segment. In this stage the embryo either remains immoveable upon the 

 bottom or slowly moves about. (In two cases delicately barbed setae, to the number of 

 thirty-five, were observed projected backward from the peduncular segment.) In the fourth 

 stage the embryo becomes attached by means of its peduncular segment. The embryo is 

 still clothed with cilia, though the long pencil of cilia has disappeared. The head is 

 closely drawn to the thoracic segment, which becomes wider in transverse diameter so as 

 nearly to hide the peduncle. In the fifth stage the thoracic ring commences to fold, or 

 turn upward, upon opposite surfaces of its circumference, so as to gradually enclose the 

 head. One fold, being made slightly in advance of the other, represents the larger or ventral 

 valve. In this stage appear clusters of barbed and deciduous setae upon the anterior 

 margin ; and in a later portion of this stage the first hardened areas of the dorsal and 

 ventral plates make their appearance, and their cirri appear as blunted papillae about the 

 mouth. In the sixth stage the shell becomes rounded, the peculiar scaled structure makes 

 its appearance, and the formation of the tubules perforating the shell, and of permanent setae 

 takes place." The author adds further that " In another memoir I hope to present the 

 characters of the genitalia of the Brachiopoda. I will state here, however, that the eggs 

 not only fill the large pallial sinuses, but hang in clusters from the genital band ; from 



these parts they escape by dehiscence, and float freely in the perivisceral cavity 



The eggs are not uniform either in shape or size." Professor Morse then describes 

 in detail each of the stages, but space will not allow of his elaborate investigations being 

 proceeded with, these would demand numerous illustrations. Professor Morse mentions 

 that he was fortunate in observing a very young example of Terebratulina septen- 

 trionalis in motion. " The animal whirled quickly on its peduncle ; when at rest the 

 shells were always closed and rested on the rock, from this position it turned slowly 

 more than half way round, raising the body at the same time almost erect ; this move- 

 ment being completed, the valves would very slowly open, and the cirri expand as if to 

 perform a grasping motion ; in no case, however, were they projected beyond the margin 



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