380 ARTHUR T. MASTEliMAN. 



then more with regard to preservation of the adult than of 

 the embryo. This author has himself made a few observa- 

 tions upon the larvse and their presence in the tentacles of 

 the parent (12). 



Methods. 



The animals themselves were well preserved, probably in 

 corrosive sublimate followed by spirit, but some little diffi- 

 culty was experienced in the case of the embryos, so that the 

 study of them has failed, to elicit all that might have been 

 expected, especially with regard to the origin of the meso- 

 derm. 



The embryos were cut in series mostly with a thickness of 

 1"25 to 2 n, and were then deeply stained with hasmalum fol- 

 lowed by aqueous eosin. A very beautiful differential staining 

 resulted. Not only were the nuclei sharply defined, bat the 

 stages in development were clearly indicated, all the earlier 

 stages staining with eosin, and the later stages, especially 

 after gastrulation, becoming clearer. At the same time the 

 hypoblast always took a dai'ker eosin stain than the epiblast. 

 Such a method of staining very thin sections when applied 

 to suitably fixed embryos of Phoronis kowalevskii could 

 not fail to settle the vexed question of mesoderm formation 

 in this species, with regard to which every observer has up 

 till now disagreed with his predecessors. 



Some of the sections were made with paraffin alone, and 

 others with the celloidin-paraffin method ; the latter were the 

 more satisfactory, mainly on account of the possibility of 

 more accurate orientation. 



The Early Development of Phoronis Buskii, McI. 



It appears as far as is known to be a general character of 

 the Phoronidea to i-etain the eggs in the lophophore until 

 the early stages are passed through. In the case of P. 

 Buskii the same arrangement holds as was noticed by Pro- 



