Hyatt.] 88 [March 5, 



The primitive cavity occurs as shown by Marshal and Schultze, 

 in the young of some forms with the epithelium unciliated as in 

 the cavities of Sycones and Leucones. Such concentration implies 

 the descent of the existing Carneospongiae through a series of 

 forms having a complex gastro-vascular system and intervening 

 between the radical Archispongiae, and the existing Carneo- 

 spongiae. These, as suggested by Haeckel, may be represented to- 

 day by the Myxospongiae, whose ampullae are diverticula, open- 

 ing directly into the cloacal canals, and have a close resemblance 

 to the ampullae of the adult Sycones and some Leucones, as well 

 as the young of Carneospongiae. This stage, in which the lat- 

 eral ampullae are first formed in the young of Carneospongiae, 

 we propose to call the Ampullinula, because the name protospon- 

 gia, as defined by Haeckel, and applied to a single vase-like form 

 without spicules immediately preceding the olynthus (Calci- 

 spongiae, yol. i, p. 347) is not applicable to such an advanced and 

 complicated organism. 



A summary, or provisional classification of the stages of growth 

 in their natural succession as they might all appear in any one 

 animal, may be given as follows : After the first stages of seg- 

 mentation have formed the amphiinorula, there appears (2) an 

 amphiblastula in which this differentiation becomes less apparent 

 through the multiplication of cells in the endoblast. During 

 these two stages a segmentation cavity appears, and either 

 remains empty or may be partly filled by the rudiments of a mes- 

 oblast arising by delamination from the wall. Whether these 

 rudiments include only the granular part of the future mesoderm 

 remains to be decided. The amphiblastula has a blastulapore, 

 which becomes subsequently closed ; then (3) an amphiblastula, 

 in which the differentiation between endoblastic and ectoblastic 

 hemispheres becomes again apparent, but the cells retain their 

 rounded segmentation outlines; then (4) an amphiblastula in 

 which the cells of the ectoblast acquire flagella and become more 

 crowded, losing somewhat of their primitive aspect. The endo- 

 blast, however, still remains with smooth, comparatively unal- 

 tered cells ; then (5) a stage in which the cells of the ectoblast 

 acquire collars around the flagella and become cylindrical. Dur- 

 ing this and possibly during the preceding stage a temporary gas- 

 rula may be formed. When the invagination of the endoblast is 



