DEVELOPMENT OF AMPHIURA SQUAMATA. 129 



The Development of the Genital Organs, Ovoid 

 Gland, Axial and Aboral Sinuses in Am- 

 phiura squamata; together with some 

 Remarks on Ludwig's Haemal System in this 

 Ophiurid. 



By 



E. W. MacBride, B.A., B.Sc, 



Scholar of St. John's College, Cambridge. 



With Plates XVI, XVIT, and XVIII, 



The work which forms the subject of the present memoir 

 was carried on at the Zoological Station at Naples during the 

 six months from October, 1891, till April, 1893. 



My original intention was to study the development of the 

 genital organs in an Echinoderm, following a suggestion of 

 Mr. Sedgwick. On my arrival at Naples I found that 

 Amphiura squamata was the only form available for my 

 purpose, since this viviparous Ophiurid is the only Echino- 

 derm which breeds in late autumn (as, indeed, it does at every 

 other season of the year as well). 



In tracing the origin of the primitive germinal cells I was 

 led, as the sequel will show, to examine the development of 

 the ovoid gland, the " Centralgeflecht des Blutsystems " of 

 Ludwig, together with the sinuses in connection with it ; and, 

 as far as I can make out, a systematic account of the history 

 of these problematical organs is presented in this paper for the 

 first time. 



Before proceeding to describe the methods employed, I shall 

 sa^ a word or two as to the suitability of Amphiura squa- 



