520 THE ANATOMY OF INVERTEBRATED ANIMALS. 



Fig. 14^.— P7)al^nf!inma'mmi!Iata.—YaT\c)\i» stages in the development of the larvae, 



(After Kowalewsky.V 

 T. The ve8i( nlar morula, flartenod and about to undergo invagination :/A, blaptccoele. 



Thn large blastonieres conslitnte the hypoblast, the small oiu^^- the epiblapt. 



II. The L^1st^)la with the blastopore, or opening of invagination, eo: ch, the blasto- 

 mere.-j which constilnte the rudiment of the urochord ; dd, the lemaiuing blasto- 

 nieres of the hvpohlast. 



III. A more advanced embryo: ch, dd, as before ; c. the epiblast ; n, the nervous 

 layer of f'fe nenral cavitv. which is now open only in fror.t near ch. 



IV. An embryo with tlie caudal appendage fiistinct. The nerve-tube n is complete, 

 and the muscle-cells m are distinguishable. 



i"Wfeitere f^^tudien fiber die Entwickelung der ciufachen Ascidicn." 

 (" Archiv lurMikr. Auat.," 1871.) 



