No. 3.] PODARKE OBSCURA VERRILL. 45 i 



wedged into the angle between the posterior part of the archen- 

 teron and the ectoblast. Beside this, there are a number of 

 scattered cells lying in the narrow cleavage space. The mesen- 

 chyme cells appear to graduate both in form and position into 

 those of the germ bands. The latter appear about the time of 

 gastrulation as two bilateral masses of cells that are pushed 

 into the cleavage cavity near the blastopore. Some of these 

 appear to pass forward and give rise to the mesenchyme ; the 

 remainder form the secondary mesoblast bands." Here again 

 we have a larval mesenchyme which apparently arises from the 

 anterior ends of the germ bands, and its cells must be homol- 

 ogous with those of the definitive bands. 



In the most recent paper on annelid cytogeny, Eisig (No, 8) 

 has described a very different origin of mesoblast from what is 

 found in any other annelid. Instead of arising from 4d, the 

 definitive mesoblast (coelomesoblast) arises from 3c and 3d (it 

 would therefore be " ectomesoblast " in Wilson's sense), while 

 the larval (paedomesoblast) arises from 4d, and not from the 

 portion of 4d which in Nereis or Podarke gives rise to meso- 

 blast, but from the portion which in those forms becomes a part 

 of the entoderm wall. 



Capitella, from the large proportion of abnormal eggs found 

 in the tubes, seems to have been an especially unfavorable form 

 for the study of cytogeny. It is difficult to believe that one of 

 Professor Eisig's scientific attainments could have committed 

 so serious an error, but these results are so very different from 

 anything else that has been described, that even though bearing 

 in mind Eisig's strictures on " Die Thatsachen nicht achten- 

 den Verallgemeinerungen," one may be pardoned, for the pres- 

 ent at least, doubt whether normal specimens were studied. 

 To these differences, which are mainly of importance in a dis- 

 cussion of cell homology, I shall return later (see p. 464). Of 

 importance in this connection is the fact that, according to 

 Eisig, the two sorts of mesoderm are not absolutely distinct, 

 but that cells may migrate out from the " Coelomesoblast " and 

 become " Paedomesoblast." Eisig believes that the two kinds 

 of tissue may have originally come from a common Anlage. 

 Eisig further argues that neither can properly be said to arise 



