534 



Forty-fifth Report on the State Museum. 



(1) Protemhryo; unsegmented and segmented stages, before 

 the formation of a primary internal cavity (blastula or segmenta- 

 tion cavity); 



(2) Mesemhryo or blastophere ; a multisegmented body with an 

 internal cavity (blastula cavity) ; 



(3) Metembryo or gastrula; a concavo-convex body consisting 

 of two layers formed either by the invagination of the blastula 

 or by the duplication of its cell-layers ; , 



(4) Neoembryo; the condition of primary division into a 

 cephalic, caudal, and subsequently a thoracic lobe, with pos- 

 teriorly directed mantle and bundles of thoracic setae. 



Fig. 197.— Terebratu- Fig. 198.— Terebratulina. Segmented 

 Una. First ciliated embryos. (Morse.) 



stage. (Morse.) 



(5) Typembryo ; in which the mantle lobes have inverted and 

 are folded over the cephalic lobe ; 



(6) Phylembryo; the state in which the characters of the 

 brachiopod-type are defined. 



When the egg becomes fertilized it may either remain attached 

 to the mother and pass its early segmented stages in that con- 

 dition, as in Lacaz^lla, or it may be set free into the pallial 

 chamber or into the sea-water. Some such ova develop cilia be- 



Fia. 199.— Terebratulina. Embryos attached by the caudal segment and showing the gradual 

 inclosure of the cephalic segment by the lobes of the mantle. (Morse.) 



fore segmentation (Terebratulina) and are thus free swimmers; 

 others evidently have no means of locomotion. Where the cilia 



86 



