250 EMBRYOLOGY OF TEREBRATULINA. 



To Lacaze-Duthiers, however, is due the credit of first presenting several stages in the 

 embryology of a Brachiopod. In a memoir : upon the curious form Thecidium, from the 

 Mediterranean, he figures the egg, as well as several subsequent stages in the early history 

 of the embryo. These were found in a pouch attached to the cirri and contained within 

 the pallial cavity. The embryo is first divided into two transverse segments, then into 

 three, and finally into four segments. In one embryo he found two red ocular points 

 upon the cephalic ring, in another four red eye spots occurred. 



In one figure he represents the rings contracted upon each other, as will be seen to be 

 the case with the embryo of Terebratulina. As before, I shall give the reader a condensed 

 translation of the paper. 



The youngest egg studied had already a somewhat pyriform and elongated shape. The most striking fact 

 was the size of the cells composing it, and which themselves enclosed a great quantity of granules of rela- 

 tively very large size. The cells no doubt were the result of segmentation, and the granules must have 

 appeared during the first movements of embryonic activity, for the vitellus had only very minute granules. 



In the next stage frequently seen after the preceding, and which I have observed in the same lot of young, 

 the embryo divided into two lobes, the larger being always attached to the suspensory filament. In the 

 embryo so divided by a circular furrow, perpendicular to the longer axis, the mass has a yellow tint, and is 

 no longer composed of large cells, but is filled with yellow granulations much finer, and enclosed in smaller 

 cells. In the smaller lobe a clearer space is seen, where the cells are filled with nearly colorless granules. On 

 each side of the larger lobe also, and very near the transverse furrow, are two transparent spaces smaller than 

 the preceding, but similar in other respects. 



The larger lobe, attached, as stated, to the suspensory filament, is the anterior ; the faces cannot yet be dis- 

 tinguished ; but later it is possible to recognize the superior or inferior aspect. 



The development, therefore, commences by the appearance of the two lobes, one the anterior, with two 

 white spots, and the other with a single clear spot ; later other spots with less coloring matter appear. Thus 

 there appears near the point of attachment, on each side of the peduncle, a clear white spot, then the two 

 lateral, spots above referred to, grow longer and obliquely extend towards the centre of the lobe. 



Between these two last spots, on the line of separation between the lobes, the colored granules accumulate 

 and form these lobules, the median later extending toward the posterior lobe. 



The posterior lobe itself does not increase in proportion to the rest of the embryonic mass, but the trans- 

 parent spot begins to show what it will later become. It extends towards the place where the lobules com- 

 mence, then it becomes depressed in the middle, and will form, in fact, a real depression. There is still a gap 

 between this and the succeeding stage to be described. The two white lateral bands, near the separation of 

 the lobes, are traces of the formation of a new lobe, for the anterior lobe divides into two by a transverse 

 furrow, and these two anterior lobes always remain relatively very large, the posterior changing but little. 



At the time when this division takes place, toward the point of attachment where two other little clear 

 spots have been seen, a lobule rises, which forms the counterpart of the little primitive posterior lobe. Thus 

 the embryo is composed of four portions, two large in the middle and two smaller at the ends. 



If the embryo is examined on all sides, it is soon seen that the two poles of the ovoid embryo are bent 

 towards each other on one side, as if the two anterior lobes were curved over towards the two posterior. 

 The concave face may be considered as the inferior, and the convex, the dorsal aspect. 



The insertion of the suspensoiy peduncle is on the dorsal side of the anterior extremity, on the back of the 

 little anterior lobule, not far from the edge of the second lobe. This peduncle is cellular, and composed of 

 very distinct elements, and easy to recognize. The embryo is, therefore, suspended by the back of the head. 



The inferior side of the anterior lobule is fiat and somewhat quadrilateral in the most developed embryo seen ; 

 near the middle is a sort of oval longitudinal slit, which appears to be the mouth, although I have never seen 

 particles of coloring matter, which I have put into the surrounding liquid, penetrate this opening, but indeed 

 the embryos are still too young to feed. 



1 Annales des Sci. Nat., 4* Serie, Vol. XV., p. 317. 



