0(52 SUMMARY OF CUURENT RESEARCHES RELATING TO 



the structureless layer imitcs with the iulernal gehitinous layer of tlio 

 stalk, and the whole looks like nicsenchymo without epidermis. Impor- 

 taut changes occur in the general disposition of the enihryo ; thus the 

 mesenchyme is turned out of the general cavit}' to form with the modified 

 epidcimis the thick cortical hiyer of the calyx. The icater-vascular rintj 

 with five lobes litis thcte trifurcated, and elongated in the arc of a circle. 

 The modification of the tentacular lobes and the evolution of the vestibule, 

 th«! changes on the stuue-caual and peritoneal sacs are then described. 

 The (jut arises (1) from the cndodermic mass of which the intestinal 

 portion ojicns (witliout ectodermic invagination) on the ventral surface 

 to the right, and (2) from the oesophageal invagination which meets the 

 stomach. 



(4) Critical portion. — Dr. Barrois then proceeds to a critical review of 

 the results of jn-cvious investigators. He afterwards devotes special 

 cliai)ters to the development of the ciliary bauds, of the ten primitive 

 limy pieces, of the buccal and anal apertures. Some account is given 

 of aberrant metamorphoses. 



One of the most important results of this valuable investigation is 

 the establishment of the homology between the peduncle of the larvaj of 

 Comatula and the preoral lobe of other Echinoderms, between the calyx 

 of the former and the proper body of othi r larvae. In making a com- 

 parison between the different larva), the author emphasizes, among 

 others, the following four points. (1) The vestibular invagination of 

 the Comatula larvfe, instead of being superposed to the buccal pad, 

 occupies on the left a position exactly congruent with that occupied by 

 the amniotic cavity described by Metschnikoff iu sea-urchins — a cavity 

 namely, which incloses the five primitive tentacles of the young 

 Echinoid, and is situated in the left half of the sub-umbrella. (2) The 

 water-pore, situated at first on the left surface of the embryo, comes to 

 lie on the dorsal surface, in a position, that is to say, corresponding to 

 that in all other Echinodcrm larva?. (3) The dorsal limy plates really 

 occupy a similar position in Comatula larvas and iu other Echinoderms. 

 (■4) The same is true of the stomachic and intestinal branches of the 

 eudodermic gut. The displacement marked by the difference of position 

 of blastopore and anus, may also take jilace in other Echinoderms. Two 

 differences are to be noted : (a) in the displacement of the body proper or 

 calyx, and (h) in the fact that the ventral and dorsal surfaces of the larva 

 correspond to the ventral and dorsal surfaces of the adult, a condition 

 associated with the change of position exhibited by the two peritoneal 

 sacs. But the unity of development among Echinoderms is nevertheless 

 cmi^hatic. 



'Challenger' Comatulae.* — Dr. P. H. Carpenter completes his work 

 on the Crinoids of the ' Challenger ' by this volume, which deals with 

 the uustalked forms. One hundred and twenty species of Antedon and 

 forty-eight of Actinomctra are now known, and of these seventy-nine 

 were discovered by the ' Challenger.' The other genera of this family 

 are Eiuliocrinus, Atelecrinus, Promacliocrinus, and Thaumatocrinus ; of 

 these Fromachocrinus differs from all other Crinoids in having ten 

 primary radials to its calyx, in place of five only. 



The author deals with the morphology of the centrodorsal and calyx, 

 and the geographical, bathymetrical, and geological distribution of the 



* 'Challenger' Keports, Ix. (1888) ix. and 401 pp. (70 pis.). 



