204 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



scent lie in an equatorial position, that one which is nearer the median 

 plane will be given the lower numeral. 



It will be noted that I follow the accepted usage, orienting the egg 

 with reference to the future axes of the embryo, and using the terms 

 dorsal and ventral in this sense. I have regarded the egg as viewed 

 from the ventral rather than the dorsal sitle, because, as is rightly 

 held, the ventral side corresponds to the ectodermal pole. 



Below is a table, the first six columns of which show the complete 

 cell lineage of the right half of the egg of Clavelina, Ascidiella, or 

 Ciona through the sixth generation (32-cell stage). The terminology 

 of Van Beneden et Julin for the 32-cell stage is given in the seventh 

 column, for purposes of comparison. In the next column is given, in 



Cell Lineage of the egg of Clavelina, Ascidiella, or Ciona, 

 right half only, through the 32-cell stage. 



First 

 Gen. 



ABCD 



1-celI 

 stage. 



Sixth 

 Gen. 



( A6-1 

 \ A6-2 



. A«-3 

 I A«-^ 



j a6-5 

 \ a6.6 



I '■'■' 



D6.1 



DO-' 

 D«3 



Y)M 



,16.5 

 flG.6 

 (l>;-7 



d6-« 



.32-cell 

 stage. 



CLAVELINA. 



Termi- 

 nology 

 of V B. 

 et J. 



Sixth 

 Gen. 



XIV 



1 



XV 



10 



2 



3 

 9 

 4 



XVI 

 XIII 



VIII 



11 



12 



6 



5 



.32-cell 

 stage. 



Interpretation of 

 V. B. et J. 



Their 

 Terminology. 



6th, 7th, 



and 8th 



Gen. 



20 

 14 

 1 

 21 

 15 

 10 



17 



11 



12 



6 



5 



44-cell 

 stage. 



My 

 Termi- 

 nology 



6th,7th. 



and 8th 



Gen. 



A"-l 

 AT.2 



AS-2 



A7.5 



A'-6 



A6.4 



q6-5 



a6-7 



I>8.1 



1)8-2 

 D7-2 

 D7-3 

 D7-4 



D63 

 D77 



d«-5 



d8-6 

 d6.7 

 ^6.8 



My In 



terpre 

 tation 



6th & 

 7th 

 Gen. 



a6.t> 

 a'i.5 



A'i-2 

 n.B-8 



A7-2 



A7.1 



A7-7 



A7-5 

 dti.8 

 (16.7 



D«-3 



d6-« 

 DV4 



D7-2 



D"-8 



D7-7 

 d6.5 



A7.6 



D"-3 



44-cell 44-ceIl 

 ;age [stage. 



