parent or before, is not settled. In a few hours after they are 

 discharged the embryos hatch and become clothed with cilia. The 

 earliest stages of the egg of Brachiopods before the larva hatches, 

 were studied by Kowalevsky after the publication of Morse's re- 

 searches. The Russian zoologist observed in the egg of The- 

 cidium the total segmentation of the yolk (also observed in Tere- 

 bratulina by Morse), until a blastoderm (ectoderm) is formed 

 around the central segmentation cavity, which contains a few cells. 

 The similar formation of the blastoderm was seen in Argiope, 

 but not the morula stage. After this the ectoderm invaginates 

 and a cavity is formed, opening externally by a primitive mouth. 

 The walls of this cavity now consist of an inner and outer layer 

 (the endoderm and ectoderm). This cavity eventually becomes 

 the digestive cavity of the mature animal. After this the devel- 

 opment goes on as previously described by Morse, Kowalevsky's 

 discoveries confirming those of the former observer. 



In Terebratulina Morse observed that the oval ciliated germ 

 became segmented, dividing into two and then 



tuft of long cilia on the an- 

 terior end (Fig. 191, A). 

 In this stage the larva is 



pidly about in every direc- 

 Soon after, the germ 



i.arvai stages or Terebratulina. loQseg itg ciUa and becomes 



attached at one end as in Fig. 191, B (c, cephalic segment; th, 

 thoracic segment ; p, peduncular or caudal segment) . The tho- 

 racic ring now increases much in size so as to partially enclose 

 the cephalic segment, as at Fig. 191, C. The form of the Brachi- 

 opod is then soon attained, as seen in Fig. 191, D, in which the 

 head (c) is seen projecting from the two valves of the shell (th), 

 the larger being the ventral plate. 



The hinge margin is broad and slightly rounded when looked at 

 from above; a side view however, presents a wide. and flattened 

 area, " as is shown in some species of Spirifer, and the embryo for 

 a long time assumes the position that the Spirifer must have as- 

 sumed." Before the folds have closed over the head, four bundles 

 of bristles appear ; these bristles are delicately barbed like those 

 of larval worms. The arms, or cirri, now bud out as two promi- 



