Normal Plates of the Development of Lepidosiren paradoxa and Protopterus annectens. 



19 



Teeth 



Teeth 

 calcified. 



Bony 



trabe- 



ciilae at 



their 



bases. 



Digestive tract 

 and liver 



Pancreas 



Well 



devel- 



oped but 



still CO' 



vered by 



buccal 



epithe- 



lium. 



Projec- 

 ting into 



buccal 

 cavitybut 

 covered 

 by epi- 

 thelial 

 sheath. 



Oesophagus solid 



behind glottis. 



Pharynx with 



lumen in middle 



(but solid laterally) 



reaching back to 



widel)' open glottis. 



Lumen rounded in 



region of stomach 



— extending into 



midgut for short 



distance. Solid 



back to near 



cloacal region. 



Pharynx with wide 



lumen though still 



unsplit at edge. 



Oesophagus with 



small discontin- 



uous lamina. In 



stomach large con- 



tinuous lumen 



opening into wide 



irregulär lumen 



of midgut which 



Stretches back for 



some distance but 



not yet continuous 



with cloacal cavity. 



Intestine deeply 



incised by spiral 



ingrowth of mes- 



enchyme. 



Liver greatly in- 



creased in size 



extending back 



dorsal to gut on 



right side. Gall 



bladder showing 



on surface ven- 



trally. 



Liver and stomach 



have been rotated 



so that liver lies 



now to the right 



of the stomach 



which is con- 



sequently visible 



from the ventral 



side. Liver growing 



rapidly backwards. 



Oesophageal 



lumen still dis- 



continuous. 



Ventral 

 rudi- 

 ments 



present. 



Pancreas 



much 

 lobedand 

 tubulär in 

 places. In 



some 

 parts the 

 cellshave 

 assumed 

 the defi- 

 nitive 

 character 

 of pan 

 creas 

 cells and 

 are func- 

 tional. 



Visceral 

 clefts 



II widely 



open. III 



closed still 



by thin mem 



brane. IV, V, 



VI solid. 



Inter- 



pene- 



trated by 



intrusive 



connec- 



tive tissue 



with 



blood 



vessels. 



Clefts II, III 

 IV, V, VI 



open, VI by 

 very nar- 

 row chink 



Clefts II— 



VI open. (In 



other spe- 



cimens of 



this stage II 



is becoming 



closed.) 



Thyroid 



Highly 



vascular 



follicles, 



well 



devel- 



oped. 



Post- 



branchial 



bodies 



Isolated. 



Nearly 



free from 



yolk. 



Pene- 

 trated by 



blood 



vessels. 



Thymus 



Thymus 

 bud of 



cleft III 

 devel- 

 oped. 



Glottis open, 



Thymus 

 bud in- 

 creased 

 in size. 

 (Rudi- 

 ment on 

 cleft II. 

 Bryce.) 



Yolk 



gone. 



Pene- 



trated by 



blood 



vessels. 



Main 



thymus 



bud divi- 



ded into 



lobes. 



Bud also 



present 



from cleft 



IV. 



Lung 



Functional 

 Extends 



back 



about '/j 



distance 



from glottis 



to cloaca. 



Walls thin 



and mem- 



branous and 



widely di- 



lated except 



close to hind 



end where 



growing 



actively. 



Urogenital 

 System 



Three pro- 



nephrostomes 



on right; two on 



left. 

 (Normally two 

 on each side.) 



Heart 



and 



vessels 



Pronephro- 

 stomes still 

 open. Meso- 

 nephric tubules 

 much elongated 

 forming com- 

 pact gland. 

 Glomeruli fully 

 developed. 

 Archinephric 

 ducts opening 

 into cloaca in- 

 dependently on 

 each side. 



Reaches 

 back as far 

 ashinderend 

 of Spiral part 

 of gut. 



Pronephros 

 very degenerate 

 and shrunken. 



Pronephric 



Chambers re- 



duced to small 



anteriorly pro- 



jecting diverti- 



cula of 

 splanchnocoele, 



on the 



walls of which 



traces of the 



degenerate 



nephrostomes 



are still visible. 



Archinephric 



ducts unite 



posteriorly and 



common por- 



tion is dilated 



bulging slightly 



forwards as 



rudiment of 



cloacal caecum. 



Ventri- 

 cular 



sponge- 

 work 



present. 



Myo- 

 tomes 



Outer 

 wall 

 thick, 

 many 



layers of 

 muscle 



cylinders. 



Splancfano- 

 cocle 



Ventral 



com- 



muni- 



cation 



between 



pericar- 



diac coe- 



lom and 



main 

 splanch- 

 nocoele. 



Pericar- 

 liac coC' 

 lom shut 

 off from 



main 

 splanch- 

 nocoele. 



Stage 



34 



35 



36 



3* 



