ox DF.VELOP^rENT ETC. OF PIIOROXTS. '")85 



Postscript. 



AVhilo the nininiscrijU, of tlio present article wns niidergoini: 

 revision, I was iimcli ])lease(] to read TIoule's elaborate work on 

 the (levelo])nient of the Phoronidœ/-'- For tlie sake of hrevity T 

 will not here discuss the author's theoretical considerations, hut 

 will offer some remarks with regard oidy to his investigations 

 relating to developmental facts. Some of his results differ consi- 

 derably from mine and from those of previous observers. And the 

 differences are such as do not seem to be due merely to different 

 conditions in the species investigated [Phoronh ><abatiéri). 



According to Eoule's observations, the first four planes of 

 segmentation are all vertical and radial, the fifth being the first 

 that is horinzontal, thus giving rise to IH blastomeres ; and the 

 egg is composed of two sorts of larger and smaller cells from the 

 first cleavage. This differs considerably from the account given 

 in the preceding pages, which is in agreement with the studies 

 of FoETTiNGER and Masterman (1900). It is, however, very 

 difficult to decide which of the two opinions is correct or whether 

 both are correct. I am at ])resent rather inclined to the latter 

 view. As to Eoule's belief in the peculiar unequal segmentation, 

 which is said to return soon after to the equal, I fear that the 

 eggs dealt with by the author may have been somewhat premature. 

 T have often observed premature eggs undergoing a remarkal)le 

 unequal segmentati(^n when mixed in water with spermatozoa. 



With respect to the nature of plasmic corpusc/es, Roule's 

 view is certainlv identical with that of Caldwell, though he does 



* Etude sur le development embryonaire des Phoronidieiis. — Ann. d. Sei. Isat. Zool., T.XI. 

 No. ]-G. 1900. 



