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two components of a syzygy are termed " epizygal " and " hypozygal." 

 The next stage to the close suture is the Loose Suture. This is either 

 overlooked by Dr. Lang, or has been confused by him with his 

 " syzygy." In the loose suture the two elements are connected by 

 fibres, as in the close suture ; but the connection is more elastic and 

 flexible, and there is a more or less developed facet cut out of the 

 edge of the plate, or else a system of ridges or striae. Finally 

 comes the Muscular Articulation, which receives a nerve supply from 

 the apical, aboral nerve centre. This is correctly described by Dr. 

 Lang, though he is wrong in saying that " all ossicles of the pinnules 

 [in living crinoids] are united by a muscle-joint." Most are united 

 by loose suture. It is also misleading to say that " where the costals 

 [i.e., primary brachials] are incorporated in the cup, a certain 

 flexibility of the calycal skeleton is the consequence." This is true 

 for the Articulata (Taxocrinus, Ichthyocrinus, and allies) ; but it is quite 

 untrue for the typical Camerata (Actinocrvius and allies). Flexibility 

 between the plates of the cup is, where it occurs, an independent 

 development, and has nothing to do with the incorporation of 

 brachials ; it is found even in some species of Inadunata, where, of 

 course, no brachials enter into the cup. 



Naturally it is difficult to draw hard and fast lines between these 

 various modes of union ; and it is a vain attempt of this kind that has 

 made the subject more puzzling than it need be. On this point Dr. 

 Lang holds a rational opinion, and exercises due caution. Perhaps 

 the whole matter may be most conveniently stated in the historical 

 or evolutionary method. The plates of Echinoderma are deposited in 

 a stroma of connective tissue fibrils, any of which may, as occasion 

 arises, assume muscularity. It is reasonable to suppose that the 

 skeleton, either in each group or in an ancestral stock, developed from 

 scattered spicules like those of most modern holothurians. This does 

 not mean that such holothurians are necessarily primitive, nor is the 

 evolution of radial symmetry, pentamerous or otherwise, now in 

 question. Spicules grew into plates or ossicles ; and these were at 

 first united loosely by the connective tissue fibrils, as yet undiffer- 

 entiated into special muscles : this first stage was the Loose Suture. 

 From this the development proceeded in opposite directions. One, in 

 the direction of greater fixity, through the Close Suture or Synostosis, 

 with its special case — the Syzygy, to the Ankylosis. The other, in 

 the direction of greater flexibility and voluntary motion, through the 

 Imperforate Articulation to the Perforate Articulation with its axial 

 nerve-cords, its highly developed muscles, teeth, and ligaments. 

 Since there is no essential difference between any of these modes of 

 union, it has always been possible, as fossils give instance, for a close 

 suture to pass back again through the loose suture to a stage almost 

 worthy the name of articulation. The stem of a crinoid, for example, 

 presents us with instances of ankylosis, close suture, syzygy, loose 

 suture, and complete articulation, each, as need arises, developed 

 independently from the loose suture, which is the normal type. 



The remaining chapters, which deal with the morphology of the 

 other systems and organs of the body, and with embryology, ontogeny, 

 and phylogeny, appear to present a remarkably exhaustive digest of 

 our knowledge, so far as recent crinoids go, well up to date, and 

 interspersed with critical suggestions of some value. Exception, 

 however, has rightly been taken by previous critics to the omission of 

 the names of authorities. One does not necessarily want a historical 

 sketch ; but the value of some of the paragraphs would be greatly 

 enhanced if one could tell on whose authority certain statements or 



