284 Brown — Developmental Stages in Streptelasma rectum. 



the individual figured this pair of septa were distinctly attached 

 to the dorsal side of the alar septa and the point of attachment 

 moved inward as the septa developed. I have before me indi- 

 viduals which show distinctly this arrangement and also one or 

 two that appear as if they might have developed after the man- 

 ner described by Carruthers. 



The question at issue, however, is, are there four or are 

 there six primary septa % Carruthers states that at the close 

 of his stage III there is a distinct pause and that no more new 

 septa appear for some time. No such pause was observed in the 

 development of Streptelasma rectum. In the majority of indi- 

 viduals of this species a second pair of secondary septa have 

 made their appearance before the first pair of secondary (Carru- 

 thers' second pair of lateral primary) septa are fully developed. 



The figures in the plate illustrating Carruthers' paper are in 

 agreement with my observations, fig. 2 being almost identi- 

 cal with fig. 1 of this paper, and showing the four primary 

 septa all equally developed and no indication of any others. 

 Fig. 3 also shows the four primary septa well developed, and 

 any indication of a third pair of septa that it may show can 

 be interpreted as a first pair of secondary septa, and no other 

 interpretation seems plausible. 



On one other point I beg to differ from Carruthers and to 

 agree with Duerden, and that is in regard to the orientation of 

 figures. Duerden in his papers* has proved that cardinal and 

 ventral, counter and dorsal are synonyms, and that the orienta- 

 tion of Kunth and his followers cannot now be used in view 

 of recent studies on the morphology and relationships of the 

 Zoantharia. Carruthers makes the cardinal side the dorsal 

 side because, as he says, the first pair of primary lateral or 

 alar septa appear at this side of the corallite in advance of any 

 lateral septa at the counter side. Since in modern corals the 

 first lateral pair of entoccels appears on the dorsal surface, the 

 dorso lateral pair of exocoels arises before the ventro-lateral 

 one, and of the six primary tentacles the dorsal pair appear 

 first, he argues that that side of the polyp which develops first 

 is the dorsal side and, therefore, the cardinal side of rugose 

 corals is dorsal. In the present paper it has been shown that 

 the counter quadrants in every respect develop in advance of 

 the cardinal quadrants, and this would still be true in every 

 respect excepting the second lateral pair of septa, even though 

 the corallite was considered to have six primary septa. 



Since this second lateral pair of septa differ in no way from 

 any other pair of secondary septa, it is still contended that 

 there are only four primary septa, and that the cardinal septum 

 is ventral and the counter septum dorsal. 



Paleontological Laboratory, Columbia University. 



* See especially J. E. Duerden, The Morphology of the Madreporaria 

 VI. The Fossula in Eugosa Corals, Biol. Bull., vol. ix, No. 1, June, 1905. 



