24 Normentafeln zur Entwicklungsgeschichte der Wirbeltiere. 
No Designation Size Preparation Data Body Form Somites 
20 H.E.C. 1352 Embryo |Fixative: Aceto-corrosive. Embryo attached to blastoderm along nearly | Thirty-five or thirty-six pairs of somites. Seg- 
5.2 mm. |Section: Transverse, 6 y. the middle third of its length. Slight dorsal| mented mesoderm extends to posterior end ot 
Stain: Iron haematoxylin, Congo red. |flexure. Head bent nearly at right angles to cloaca. In cardiac and vitelline duct regions, 
dorsal line of body. Tail bent ventrally and |sclerotomes loosely mesenchymous and extend 
ending in a distinct tailknob. Pericardial cavity | dorsally to base of neural canal. In same 
forms distinct rounded swelling. region, posterior border of myotome is. fibrous. 
21 H.E.C. 1637 Embryo |Fixative: Aceto-corrosive. No dorsal flexure. Mid-brain region projects |Fifty or fifty-one pairs of somites. 
6.2 mm |Section: Sagittal, 8 n. forward beyond fore-brain region, which is 
Stain: Iron haematoxylin, Congo red. | bent backward at an angle of 30° to it. Tail 
flexed almost at right angles to trunk. Tail 
| knob not well marked. 
22 H.E.C. 15063 | Embryo |Fixative: Aceto-corrosive. ‚Mid-brain region bent at right angles to |Fifty-three ‘or fifty-four pairs of somites 
7.5 mm, |Section: Transverse, 6 u. pharyngeal. Fore-brain region bent a little |(counted from sections). Segmented meso- 
Stain: Iron haematoxylin, orange G. | posteriorly from mid-brain region. Antero- |derm extends beyond cloaca. Sclerotomes of 
ae diameter of yolk stalk one-fourth |last ten somites not yet formed. 
| ength of embryo. A very slight dorsal 
flexure over yolk stalk region. Small tail 
knob. 
I} 
23 H.E.C. 1495 | Embryo |Fixative: Aceto-corrosive. Antero-posterior diameter of yolk stalk one- | Sixty-three pairs of somites (counted exter- 
| 9.0 mm. ‚Section: Transverse, 8 u. fifth length of embryo. Mid-brain region bent |nally). Segmented mesoderm extends nearly 
Stain: Iron haematoxylin, orange G.|at right angles to pharyngeal. Fore-brain bent|to neurenteric canal. Sclerotomes of last 
at an angle of about 45° to mid-brain region. |sixteen somites not yet formed. 
Fairly prominent tail knob. 
24 a) H.E.C. 206 Embryo |a) Fixative: Aceto-corrosive. Fore-brain region flexed until original antero- | Sixty-five pairs of somites in a cleared embryo 
11.5 mm. Section: Transverse, IO u. posterior axis lies in transverse plane. Dis- | of the same size and stage. Somites anterior 
Stain: Borax carmine. tinct ’twixt-brain swelling. Sharply outlined |to pancreas not in contact with coelom wall 
b) H.E.C. 208 b) Fixative: Aceto-corrosive. branchial plate. Beginning of mid-lateral line. | ventrally. Somites in posterior trunk region 
Section: Sagittal, IO u. Pericardial chamber dilated. Cloaca forms |attached to coelom wall by a narrow solid 
Stain: Borax carmine. prominent ventral swelling. stalk. 
e) H.EA2 2207; c) Fixative: Aceto-corrosive, 
Section: Frontal, IO u. 
Stain: Borax carmine. 
25 a) H.E.C. 223 Embryo |a) Fixative: Picro-sulphuric. Fore-brain swelling farther expanded ventrally | Seventy-one pairs of somites in a cleared em- 
13.0 mm. | Section: Transverse, IO pn. than in preceding stage (No. 24). Mid-lateral | bryo of the same length and stage. 
|. Stain: Alum cochineal. line distinct from branchial plate backward to 
b) H.E.C. 224 ıb) Fixative: Picro-sulphuric. a point midway between cloaca and tail. 
| | Section: Sagittal, IO u. 
| '  Stain: Alum cochineal. 
| E)’ELE:C.226 c) Fixative: Picro-sulphuric. 
Section: Frontal, IO x. 
Stain: Alum cochineal. 
26. | a) HLE.C. 227 Embryo |a) Fixative: Picro-sulphuric. Entire head region bent a little ventrally from | Eighty-six pairs of somites in a cleared embryo 
15.0 mm. Section: Transverse, IO u. pharyngeal region. Anterior and posterior | of the same length and stage. Anterior trunk 
Stain: Alum cochineal. dorsal fins differentiated from dorsal fin fold. | somites extend into upper part of lateral body 
b) H.E.C. 229 b) Fixative: Picro-sulphuric. Pectoral fin fold present. Wide ventral fold | wall. Somites connected with coelom wall 
Section: Sagittal, 20 ı. of caudal fin. Prominent cloacal protuberance. | from level of third turn of spiral valve pos- 
Stain: Alum cochineal. teriorly. 
2), ELE:C. 228 c) Fixative: Picro-sulphuric. 
Section: Frontal, I6 u. 
Stain: Alum cochineal. 
