EMBRYOLOGICAL MONOGKAPHS. 



PLATE I. 



Development of the Hvdroida. Figures from Nicolaus KLEiNExnERC, and George J. Allman. 



C. cav. Cavity of the pl.inula. 



cp. "Structureless ciiiisule." 



£. cb. Ejiiblast. 



e b'. Eiiiblastic prominence. 



e X. s. External pellicle, or perisarc. 



G. gU'. Gastric cavity. 



H. h h. Hypohlast. 



h b'. Hypolilastic elevation under tlie epihlastic. 



7. i. Internal iiellicle, or perisarc. 



M. mh. Membrane. 



K.nl. Knek-us(?). 



0. ovi. Ovum. 



or'. Thin region of walls at one pole where a 

 mouth is later formed. 



T. t.a. Permanent tentacular processes. 



ta'. Provisional tentacular appendages. 



f. Sucker-disk at "proximal" extremity. 



Tj. Situation of mouth at " distal " extremity. 



6. ('elhdar bodies surrounding the ovum. 



X. Orifice formed by an invagination of a ten- 

 tacular process (/ a'). 



fju. Chamber fdlcd with " granular proto- 

 plasm." 



0. Diverticulum from the cavity of the blas- 

 tostylc from which the hernia-like bud 

 forms. 



w. Highly refractile body. 



1-11. Development of Hiidrn, from Kleinenbei'g, Hydra. Eine Anatomi.sh — Entwicklungsgeschichtliche 

 Untersuchung. Ph II., Figs. 10, 11, 16, 17, 18, 19 ; Ph 111., Fig.s. Ij, 12, 1.3, 14, 15. 



1. Ovum of //. anrantificn, in amceboid condition, with chlorophyll granules and yolk spherules (pseiidocells). 



The large cell in the center of the figure is the germiuativc vesicle. " Der Keimtleck des Keimblaschen ist 

 in der Fig. nieht zu sehen, war aber noch vorhanden," Kleinenberg. The processes thrown out in all 

 directions are protoplasnuc. Tlie yolk cells are formed from the protoplasm. 



2. Gcrminative vesicle .liber.ited from the enveloping substance. mb. Membrane. nl. Gerniinative dot. 



a. Refractile body in the gerniinative dot. 



3. Ovum shortly before the rupture of the surrounding cells (6). om. Ovum. 



4. Segmented ovum with two spheres. 



5. Still older ovum, with four spheres. No segmentation cavity is formed. 



6. Morula. 



7. Section through the gerniinative vesicle of //. viridis. ex. s. External pellicle, rjn.. Body cavity, i.s. In- 



ternal Iiellicle. 



There is a layer of cells surrounding the body cavity inside the internal pellicle. The external pellicle 

 (perisarc of marine hydroid ?) is ultimately lost ; the internal is absorbed. 



8. Y.mh\yo o{ H. aurmitinca. eh. Ejiiblast. hb. Hypoblast, i.s. Internal pellicle. The external pellicle is 



ruptured and thrown off. The caudate cells ("nerve-muscular") form in the outer layer {eb). The inner 

 layer {hb) in this stage becomes cidUihir. 



9. Embryo of last-named species, seen in )ilane of longer axis. The future nmuth opens near or', eb. Epiblast. 



hb. Hypoblast, i.s. Internal pellicle. 

 10. The same with the walls of the two poles sinnlar. cb. Epiblast. hb. Hypoblast, i.s. Internal pellicle. 



