420 NATURAL SCIENCE. June, 



the food-groove, both in arms and pinnules. They vary considerably 

 in the extent of their development ; but they occur in almost all 

 crinoids, and the species in which they are so atrophied as to be 

 indistinguishable are very few indeed. They close over the food- 

 groove, so as to protect its delicate ciliated lining from mud or other 

 destructive agents; but during active life they are kept open. They 

 are more highly developed in many of the Palaeozoic crinoids than in 

 those of our own day, and are, in some of the former, very complicated 

 structures ; but even here there is evidence that they could be opened. 

 I have myself figured specimens of Botvyocrinus from the Wenlock 

 limestone preserved with the covering-plates erect, which is direct 

 evidence, and I have demonstrated in Cyathocrini from Gotland the 

 presence of an articular facet and apparent innervation from the 

 axial nerve-cords, which is indirect evidence. Consequently, Dr. 

 Lang is speaking far less than the truth when (on p. 890) he refers to 

 the Inadunata as possessing covering-plates, which "could probably 

 be erected," in non-pinnulate arms alone; or when (on p. 960) he 

 speaks of covering-plates in the past tense only, and of their absence 

 as quite a common occurrence. 



The section on the Mode of Union between the skeletal pieces 

 (pp. 964, 965), betrays a hopeless confusion, perhaps pardonable con- 

 sidering the difficulty of the subject. The first mode of union is thus 

 described. " Two plates are firmly and immovably joined. There is 

 no fibrous connection between them ; between the two plates is an 

 unbroken deposit of calcareous substance, which, however, is less 

 solid than that of the plates themselves." So far, so good ; this is a 

 fair enough description of fusion or ankylosis, such as obtains between 

 the basals of Bathycvinus or the radials of Rhizocvinus. But mark how 

 our author proceeds ! " In this way all or some of the plates of the 

 cup are frequently united, e.g., the radials of Antedon with one another 

 and with the centrodorsal. Such a union is called a suture or 

 synostosis." This is entirely incorrect. The term "suture" is a 

 general one, which may be applied to every mode of union short of 

 muscular articulation. The union above described is an ankylosis, 

 not a synostosis. The radials of Antedon are not united in this way, 

 but are united by " synostosis," or Close Suture, as Carpenter, 

 vYachsmuth and Springer, and myself subsequently preferred to call 

 it. In a close suture (I quote P. H. Carpenter) the skeletal elements 

 are united " by means of connective tissue fibres, which pass from 

 the . . . organic basis of the one joint into that of the other. 

 These fibres are sometimes quite short, and their ends are surrounded 

 by the denser layers of calcareous reticulation on the apposed surfaces 

 of the two joints, which are thus closely and immovably fitted together, 

 though they can be separated by the action of alkalies." This kind 

 of suture is probably that which Dr. Lang had in his mind when he 

 penned his next paragraph, in which he erroneously calls it a Syzygy. 

 It is true that a syzygy is a form of close suture ; but it is untrue 

 that "all or most of the ossicles of the stem are united by syzygial 

 sutures," that " syzygial sutures may occur in the cup," or that "the 

 occurrence of syzygial sutures in a series of ossicles renders a certain 

 flexibility possible." The term " syzygy" was invented by Johannes 

 Muller, and by him applied to that particular case of close suture 

 between two brachials in which the proximal or lower of the two 

 loses its pinnule (supposing pinnules to occur). The term has since 

 been extended to the precisely parallel case of close suture between 

 two columnals, in which the lower of the two loses its cirri (supposing 

 cirri to occur on all columnals), while the upper still bears them. The 



