Anatomy, Physiology, Embryology. II. Pelmatozoa. J 85 



and its communication with the exterior through the madreporite is not yet satis- 

 factorily proved in the other Echinoderms, so that Perrier's generalisation is at any 

 rate premature. 



Howell mentions a Holothurian found at Beaufort, U. S., in which the water- 

 vascular system and body-cavity contain, besides colourless amoeboid corpuscles, 

 a large number of red ones, oval, nucleated, and bi-convexin shape. Their colour- 

 ing matter has most of the essential properties of vertebrate haemoglobin, but 

 differs from it slightly in the albuminous portion of the molecule. 



Metschnikoff defends his previous views respecting the unsymmetrical origin of 

 the Mesoderm cells in Echinoderms [see Bericht for 1884 Ipl71]; and he 

 criticises Selenka's latest observations [see Bericht for 1883 I p 126]. In the 

 gastrula of Astropecten the cells at the blind end of the archenteron become 

 flatter and form an epithelial layer. Some put out pseudopods, and eventually 

 four, five, or more separate themselves from the epithelium and enter the cleavage- 

 cavity as the first wander-cells or Phagocytes. The number of these does not 

 increase by division , but by the addition of new elements from the epithelial 

 layer, gaps in which are, however, filled up by cell-division. Emigration ceases 

 when the coelomatic vesicles are formed, though the epithelium cells long con- 

 tinue to put out pseudopods. In Sphaerechinus granular is and Strongylocentrotus 

 (Toxopneustes) lividus cubical or cylindrical cells enter the cleavage-cavity from 

 the blastoderm and mostly increase in number by continued emigration, but they 

 never have any symmetrical arrangement. Emigration thus commences earlier 

 than in the Asterids (i. e. before invagination) and as the same is the case in the 

 Ophiurids it must be connected with the skeleton-forming function of the Pha- 

 gocytes. The mode of their development is relatively more primitive than in the 

 Ctenophora [antea, p 166]. 



Nachtrieb finds that in the Gastrulae of Ophiothrix and of many Urchins the 

 ectoderm is thickened at the pole opposite to the blastopore and bears longer 

 cilia than elsewhere. The praeoral band of cilia in Bipinnaria is possibly a modi- 

 fication of this structure. ' The immature eggs of Moira were seen to thrust out 

 pseudopodia through the egg membrane , after being mixed with active sperma- 

 tozoa, and afterwards withdraw them again. Both in Moira and in Ophiothrix 

 segmentation becomes irregular after eight blastomeres are formed. - - A com- 

 parison of the origin of the body cavity and water-vascular system in the different 

 classes places them in a rising scale with the Holothurians in the lowest, the 

 Starfish in the middle and the Crinoids in the highest position. 



II. Pelmatozoa 



(including Crinoidea, Cystidea, and Blastoidea). 



See also Marshall (*, 2 ) supra, p 184, v. Graff, and Carpenter ( 7 , 8 ). 



Carpenter ( ] ) gives an extended account of the morphology of the Crinoidea 

 under the following heads. 1. The Skeleton generally, with the modes of union 

 of its component joints. 2. The Stem and its Appendages. 3. The Calyx. 

 4. The Rays. 5. The Visceral Mass. 6. The Minute Anatomy of the Disk 

 and Arms. Three types of stem occur in recent Crinoids, viz. that of the Penta- 

 crinidae with syzygies at the nodes; that of the Bourgueticrinidae and the ex- 

 tinct Platycrinus with radicular cirri or a branching root; and that of Hyocrinus 

 which also occurs in many Palaeocrinoids. The radials of Thaumatocrinus are 

 separated by interradials which rest on the basals below. But in every other Neo- 

 crinoid they form a closed ring, and the interradials, when present, rest on their 



