EXPLANATION OF PLATES I TO XLVI. 



Unless it is otherwise stated, the colors in the plates designate the following 

 structures : Red, the endoderm and organs which are endodermal in origin, and also, 

 in the figures of eggs and embryos, the epithelial capsule and the structures which are 

 derived from it ; blue, the follicle, and the structures which are derived from it ; 

 yellow, the body cavity, the heart, and the blood spaces; green, the perithoracic 

 tubes, and cloaca or atrium; purple, the endoderm and its derivatives; orange, the 

 eggs and the blastomeres. 



In Plates IX, X, XI and XII, the perithoracic tubes and the median atrium or 

 cloaca are colored red, while they are colored green in all the other plates. 



a, Ectoderm. 



a', Ectodermal layer of 



stolon. 



a", Reflected layer of ecto- 

 derm around the root 

 of the stolon. 



"', Ectodermal blastom- 

 eres of embryo. 



b, Endoderm. 



b', Epithelial capsule of 

 embryo. 



c, Pharynx. 



cb, Peripharyngeal band. 

 eg, Dorsal tubercle. 



d, Endostyle. 



d 1, Right half of endo- 



style. 



d 2, Left half of endostyle. 

 d', Endodermal tube of 



stolon. 



d". Wall of endodermal 

 tube of stolon. 



e, Heart. 

 em, Embryo. 



end, Endostyle. 



/, Pericardium. 



g, Right perithoracic tube 

 of the stolon and of 

 the aggregated salpa. 



g', Perithoracic tubes of 

 embryo. 



REFERENCE LETTERS. 



g", Spiracle or external 

 opening of perithor- 

 acic tube. 



g"', Median atrium or clo- 

 aca. 



g lv , Gill-slits. 

 <7 T , Atrial or cloacal aper- 

 ture. 



h, Left perithoracic tube 

 of stolon and of ag- 

 gregated salpa. 

 i, Lower blood tube of 



stolon. 



int, Intestine. 

 j, Upper blood tube of 



stolon. 

 k, Eleoblast. 

 I, Nerve tube of stolon. 

 m, Follicle. 



ft, Ovary or eggs. In 

 Plate III, Fig. 3, the 

 nucleus. 

 o, The dorsal lamella or 



"gill." 

 p, Intestine. 

 p', Stomach. 

 P", Anus. 

 pi, Placenta. 



ph, In Plate IV, oesopha- 

 gus. 

 r, Peripharyngeal bands. 



s, Ganglion. 

 st, Stolon. 



t, Subneural gland. 



, Muscles. 



v, Cellulose mantle. 



w, Oral muscles. 



x, Fertilizing duct. 



x' , Testis. 



y, Blood-spaces. 



y' , Cavity between the 

 two folds of embryo 

 sac. 

 y", Cavity of placenta. 



z, Mouth. 



1, 2, 3, 4, Primary blasto- 

 meres. 



5, Primary cavity of folli- 



cle. 



6, Proliferating area of 



follicle. 



7, Somatic layer of folli- 



cle. 



8, Visceral layer of folli- 



cle. 



9, Blastoderm cells 



9', Endodermal blastom- 

 eres. 



10, Placental portion of fol- 



licle. 



11, Opening of fertilizing 



duct. 



