Octobee 3, 1884.] 



SCIENCE. 



341 



layers being quite distinct. In pelagic eggs the pro- 

 cess is quite different. Sections of the eggs of Trachi- 

 nus vipara at this stage show that the parablast of 

 Klein, the intermediate layer of American authors, is 

 made up of a large number of free cells, and nuclei 

 are absorbed from the yolk, which contribute to a very 

 great extent to build up the hypoblast. In this case, 

 there is no true invagination. In Motella mustella 

 the origin of the hypoblast is similar to that of 

 Trachinus; but the resulting cells, instead of being 

 quite similar to the original ones as usual in teleos- 

 tean eggs, are very much larger, and hexagonal, so 

 that they cannot be derived directly from the lower 

 layer of cells. The author sustained the views of 

 Ryder as regards the segmentation cavity in pelagic 

 eggs. He also holds that there is no circulation in 

 pelagic embryos before hatching. 



Mr. G. Macloskie, in his paper on the dynamics of 

 the insect crust, commenced with a general descrip- 

 tion of the chitinous skeleton with its in- and out- 

 growths, etc. The tracheae have spiral crenulations, 

 which have been hitherto misunderstood and sup- 

 posed to be threads; these tracheae transmit gases 

 directly to the tissues, and the blood is not used for 

 this purpose. The tracheae are not directly controlled 

 by muscles ; their action depending on the successive 

 production of a partial vacuum, and condensation of 

 air around them. 



Prof. A. Hyatt read a paper on the larval theory 

 of the origin of tissue, stating that the building-up of 

 the tissues of the metazoa is due to a quick and 

 rapid division of cells. Minot's theory that the ori- 

 gin of the sexes is due to the difference in cell ele- 

 ments was supported. The author considered the 

 planula a more primitive form than the gastrula. In 

 another paper Professor Hyatt presented objections 

 to some commonly accepted views of heredity; assert- 

 ing that heredity has no need of the gemmule hy- 

 pothesis or pangenesis, but that it can be equally well 

 understood upon the supposition that the nuclei of 

 cells are the immediate agents of the transmission of 

 characteristics. The author presented the case of a 

 man in Maine who resembled the mother on one side 

 of his body, and his father on the other side, as an 

 illustration of his theory; and he contested the posi- 

 tion of Professor Brooks as regards heredity. In a 

 paper on the structure and affinities of Beatricea, the 

 same author stated that this fossil has had many posi- 

 tions assigned to it in almost all the groups of the 

 Invertebrata, though he himself now thought it a for- 

 aminifer. Thin sections were examined, the struc- 

 ture being found to consist of cells joined by a stolon. 



Dr. C. S. Minot presented a paper on the skin of 

 insects. The skin consists of three layers, — exter- 

 nally the cuticula, overlying an epithelium, which lies 

 in turn on a sheet of connective tissue; the epithe- 

 lium, homologous with the epithelium of other ani- 

 mals, and which should be so called instead of hy- 

 podermis; and dermis, which name should be applied 

 to the connective tissue, as it is the homologue of 

 that of vertebrates. The cuticula of caterpillars has 

 not yet been fully described: it consists of two layers, 

 a thick one and a thin one. 



In a communication on the development of Limu- 

 lus, Mr. J. S. Kingsley stated that his account begins 

 after the formation of the blastoderm. At this time 

 there is a single layer of cells surrounding the yolk, 

 in which are scattered nuclei. The mesoblast arises 

 as a single sheet on the ventral surface. Its cells come 

 largely from the blastoderm, but some arise from 

 the yolk nuclei. The mesoblast soon forms two lon- 

 gitudinal layers, one on each side in the neighbor- 

 hood of the limbs. The coelom is formed by a split- 

 ting of the mesoblast, and at first consists of a series 

 of metameric cavities extending into the limbs. The 

 supraoesophageal ganglion arises by an invagination of 

 the epiblast. The heart arises as two tubes in the 

 somatophore, which later unite. The mesenteron 

 does not appear until after hatching. The amnion 

 of Packard is the first larval cuticle, and bears a 

 resemblance to the amnion of the tracheata. A sec- 

 ond cuticle is formed and moulted before hatching. 

 The eyes appear on the dorsal surface at the same 

 time that the limbs appear on the ventral. In these 

 characters Limulus agrees essentially with the trache- 

 ata, and has nothing in common with Crustacea. 



Prof. B. G-. Wilder, in a paper entitled, ' Do the 

 cerebellum and oblongata represent two encephalic 

 segments, or only one?' remarked that most writers 

 had considered two segments to exist. The cephalad 

 of these segments is held to include the cerebellum, 

 together with the portion of the 'brain-stem- imme- 

 diately connected therewith and the latter part of the 

 oblongata. The only writers that have admitted of 

 a single segment caudad of the mesen are Balfour, 

 A. M. Marshall 1 , Owen, and Spitzka. The vitws of 

 Spitzka were then discussed; concluding with the 

 opinion that sufficient evidence to settle the question 

 was wanting. 



Dr. J. A. Ryder presented a paper on the morphol- 

 ogy and evolution of the tail of osseous fishes. The 

 caudal fin of fishes is developed in the same way as 

 the other median or unpaired fins, from a median 

 fin-fold. After the protocercal stage of the larva is 

 passed, a lower caudal lobe grows out, which is proba- 

 bly the homologue of a second anal fin. The hypoth- 

 eses which grow out of a consideration of the facts 

 of the development of the tails of fishes, are the fol- 

 lowing: 1. Whenever heterocercality manifests itself, 

 there is a more or less extensive degeneration of the 

 caudal end of the chordal axis, which began to be 

 somewhat manifest far back in the phylum in such 

 forms as Holocephali, Dipnoi, and crossopterygians. 



2. With the outgrowth of the lower lobes (second anal) 

 the energy of growth tended to push the tip of the 

 chorda upward; the lobe itself arising, probably in 

 consequence of the localization of the energy of 

 growth and the deposit of organic material at the 

 point according to the demands of use and effort. 



3. Local use and effort, acting as constant stimuli of 

 local growth, carried the heterocercal condition and 

 its accompanying modification of degeneration and 

 reduction still farther, as is shown by a study of the 

 homologous elements in the tails of fishes; while 

 use and effort would also continue to augment hetero- 

 cercality, until the inferior and superior lobes were 



