1904.] NATURAL SCIENCES OF PHILADELPHIA. 729 



Postscript. 



Since the above paper was presented for publication there have come 

 to hand two papers by Prof. John H. Gerould: "The Development of 

 Phascolosoma " {Arch. Zool. exp. et gen. 11, 2, 1904) and " Studies on 

 the Embryology of the Sipunculidse: I. The Embryonal Envelope 

 and Its Homologies " {Mark Anniversarj/ Volume, Art. XXII). In 

 the former of these two papers Prof Gerould shows that in Phasco- 

 losoma the ectoderm arises from the first three quartettes of micro- 

 meres, the mesoderm from 4d, and the entoderm from the remaining 

 cells, thus adding a representative of the Sipunculids to the list of 

 forms mentioned in section IV (4) of the present paper. The author 

 further points out the presence of a typical annelid "cross" and 

 "rosette" in Phascolosoma, that the prototroch of the larva is formed 

 from the sixteen "primary trochoblasts," and that the "somatic 

 plate" arises from 2d. The second paper mentioned, among other 

 interesting facts concerning the relation of the larva of Sipunculus 

 and Phascolosoma, establishes the homology of the "serosa" of 

 Phascolosoma with the prototroch of Sipu7iculus. 



