ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 655 



forms ; the first family is that of the Holopidas, under which Holopus 

 is very fully described ; the second family, that of the Hyocrinid^, 

 is new, the character of Hyocrinus being sufficient to distinguish it 

 from the Apiocrinidte ; de Loriol's family name of Bourgueticrinidfe 

 (188"2) is accepted for Bathycrinus and Bhizocnnus, the characters 

 of which are emended. In the Pentacrinidse there is the new genus 

 Metacrinus for forms which appear to be confined to the Eastern seas. 

 Various problems are discussed in an appendix, and the whole work 

 concludes with a full bibliography of the Neocrinoids and an excellent 

 index. 



Development of Comatula.* — Professor E. Perrier in a preliminary 

 notice brings forward the following facts concerning the organogeny 

 of Comatula. 



From the archenteron are developed three diverticula ; two 

 form the general body-cavity, while the third gives rise to the 

 ambulacral ring ; directly the latter is formed it communicates with 

 the exterior by a single " stone canal." The rudiment of the structure 

 termed by Ludwig the dorsal organ arises by a columnar thickening 

 of one of the layers of the right peritoneal sac ; round the prolonga- 

 tion of the right peritoneal sac into the axis of the peduncle the 

 mesodermic tissue becomes differentiated into the chambered organ ; 

 a similar differentiation takes place in the walls of the calyx to form 

 five cords, which pass to the septum, separating the two halves of the 

 body-cavity ; these cords as well as the two peritoneal sacs and the 

 ambulacral sac share in producing the rudiments of the arms, which 

 thus contain (1) an ambulacral canal, (2) a subambulacral cavity con- 

 tinuous with the left peritoneal sac, and (3) a much smaller cavity 

 connected with the right peritoneal sac ; later this cavity enlarges 

 and a new cavity — the genital space — appears between it and the 

 subambulacral cavity. The young Comatula is set free at the period 

 when each arm has only a single pair of pinnules ; there are at that 

 time five " stone canals " which open directly on to the exterior ; 

 these tubes generally rupture at the point where they enter the body- 

 walls, and ajipear therefore to open into the body-cavity, which they 

 never do in reality, even in tlie adult. At the same period of deve- 

 lopment a number of fibro-cellular cords appear around the oesophagus 

 and along the dorsal organ, which form a plexus of vessels which 

 send off branches, some opening on to the exterior of the body, and 

 some into the body-cavity and into the ambulacral vessels ; a plexus 

 of these vessels envelope the dorsal organ, and has been comjiared by 

 Glaus with the heart of sea-urchins and star-fishos. The ambulacral 

 system, therefore, together with these vessels, forms a single vascular 

 systom functionally one, though devolopmentally composed of two 

 distinct and separate systems. The dorsal organ is prolonged into the 

 arms and into the pinnules, and forms the genital rachis ; the dorsal 

 organ itself consists of pyriform colls which come to be grouped 

 round a central cavity ; this gives off short diverticula, and transverse 



♦ Zool. Anzcig., viii. (ISSO) pp. 2G1-0. 



