i8g 5 . NOTES AND COMMENTS. 375 



and ventral parts of the skeletogenous elements formed from two 

 protovertebrae. This alteration of relations has been known for long, 

 and is always referred to, as the resegmentation of the body, the 

 teleological explanation being that the muscles must pull upon two 

 vertebrae in order to make the whole segmented organism a physio- 

 logical unit. But, according to Dr. Gadow, it takes place in a 

 manner fundamentally different to what has been supposed. Each 

 new or permanent skleromere is not formed by the vertical splitting 

 of two successive sklerotomes, but is composed of the dorsal half of 

 the posterior and the ventral half of the more anterior sklerotome. 



Apart from the interest of this for vertebrate morphology 

 generally, it has a biological interest that may appeal to many 

 naturalists who neither know nor care to know the details of the 

 embryological history of the skeleton and musculature. For it is one 

 of the many instances in which the doctrine of a sudden and inexpli- 

 cable (save teleologically) change has been abandoned after minuter 

 investigation for a doctrine of slow metamorphosis. It is almost 

 impossible to believe, if one reflect upon it, that " resegmentation " 

 actually could occur, that the primitive myotomes, having been 

 formed, should be cut in two, and that the adjacent halves of 

 successive myotomes should unite. But some such theory as that 

 was accepted unquestionably for long, and, so far as we know, it has 

 not been criticised before the appearance of this paper by Dr. Gadow. 



A Monograph of Crinoids. 

 The crinoids of the Palaeozoic rocks of North America are so 

 rich and varied in form, so numerous in individuals, that they have 

 long been the delight and the despair of naturalists. Especially is 

 this the case with that order of the crinoids to which the name 

 Camerata is now generally applied, the order that includes such well- 

 known forms as the Nave Encrinite, Actinocrinus, the Rose Encrinite, 

 Rhodocrinus, which are common enough in our own Mountain Lime- 

 stone, together with the flatter and simpler form, Platycrinus. For, 

 in America, there are added to these ordinary genera such remark- 

 able creatures as the huge Megistocrinus, the speared and spined 

 Dorycrinus, the peculiar mushroom-like Agaricocvinns, Stvotocvinus like 

 a college don in his mortar-board, Eretmocrinus with its broad oar-like 

 arms, Pterotocrinus whose lofty dome is surmounted by wings, 

 Gilbertsocrinus with strange drooping appendages of unknown 

 function, and Batocrinus whose pores at the bases of the arms are 

 equally mysterious. But this list does not include a quarter of the 

 camerate or vaulted genera known from the Carboniferous rocks of 

 America alone ; while, if we accept the work of Mr. S. A. Miller and 

 kindred spirits, the long line will stretch out to the crack of doom. 

 Such, indeed, is the variety of form, and such the rashness of 

 interpretation of some of the more enthusiastic collectors and 

 describers, that to us European students the subject has become one 



