566 E. W. MACBRIDE. 



that its most anterior lobo^ numbered 1 by Grave, lias not 

 only passed over tlie CKSophagus to tlie riglit, but has con- 

 tinued its revolution underneath it to the left again, so that 

 it has been rotated through an angle of 180°, whilst the most 

 posterior lobe, No. 5, has rotated through 90° only, the whole 

 hydroca3le having grown longer. The left anterior coclora, 

 together with the madreporic pore which has now appeared, 

 follow the rotation of the hydrocoele and pass over the 

 esophagus on to the right side. The lobes of the hydrcocle 

 become trifid, the lateral lobes being the rudiments of the 

 first paired tube-feet. 



From the left posterior coelom, termed by Grave the 

 " hypogastric,'^ there arise four out-growths, which, insinua- 

 ting themselves between the lobes of the hydrocoele, form the 

 rudiments of the radial perihtemal canals and of theperiha3mal 

 ring in the same manner as I have descidbed in Asterina 

 gibbosa. A fifth is given off from the left anterior coelom. 

 In later stages the nervous system makes its appearance as 

 thickenings of the neutral ectoderm overlying the ring and 

 radial canals. These thickenings are then invaginated into 

 grooves and so the epineural canals of the adult are formed. 

 The larval organ gradually disappears, but the young 

 Ophiurids retain for a considerable period some of the larval 

 transverse rings of cilia. 



I have described Grave's work at some length, since it is 

 the latest work of any importance on the formation of organs in 

 an Ophiurid which has been published. Making allowances for 

 differences in nomenclature, it will be seen that Grave confirms 

 Bury in the opinion that the hydroccjele springs from the left 

 posterior coelom. The independent origin of this portion of 

 the coelom as a separate evagination of the gut from that 

 which gives rise to the two anterior ca'lomic vesicles is 

 almost unique in the published accounts of Echinoderm 

 development. It is true that Mastermau (20) has described 

 a somewhat similar state of affairs in a star-fish, Cribrella 

 oculata, in which, according to him, the hypogastric coelom 

 (left posterior coelom) docs not arise from the common rudiment 



