382 



SCIENCE. 



[Vol. II., No. 82. 



near Kutais. A large number of new species and 

 varieties are described. — {Jahrb. mal. ges., vii. ii.) 

 w. H. D. [230 



Monograph of Ringicula. — L. Morlet has pub- 

 lished a secund supplement to his valuable mono- 

 graph of Kingicula, in which four new recent and as 

 many new fossil forms are made known, and a synop- 

 sis, after Seguenza, of the tertiary Italian species, is 

 added. — {Journ. de conchyl., xxii. 3.) w. h. d. [231 



Worms. 

 Nevsr -worni •writh remarkable nervous system. 



— Tlie Willem Barents on her third voyage captured 

 a worm, which A. A. W. Hubrecht describes under 

 the name of Pseudonematon nervosum. He gives a 

 general account of its structure, and promises a fuller 

 monograph. The animal is about sixty-five milli- 

 metres long, one and tliree-qiiarters millimetres 

 thick, tapering behind. The digestive tract runs 

 straight through from end to end. On the ventral 

 side, about forty-five millimetres from the head, is a 

 disk, probably a sucker. No traces of sexual, excre- 

 tory, or sensoi'y organs were found. The epidermis 

 is thin. The muscles form three layers, — a thick 

 external longitudinal, a middle transverse or circu- 

 lar, and an internal longitudinal layer, — variously de- 

 veloped in different parts of the body. The nervous 

 system is very remarkable: it forms a continuous 

 layer completely around the body, and lies immedi- 

 ately inside the layer of circular inuscular filires. It 

 consists, 1°, of a fine network of delicate filaments, 

 appearing as if felted, barely tinged by the staining 

 reagents; and, 2°, of scattered nuclei belonging partly 

 to connective tissue, partly to ganglion-cells. The 

 layer forms a continuous tube from the head, where 

 there is no ganglionic enlargement, back through the 

 body to the caudal region, where the layer is present 

 dorsally only. 



Hubrecht further discusses the phylogeny of the 

 nervcms system in continuation of his previous paper 

 {Quart, jouni. iidr.r. n/i., xx. 431). He points out, 

 that, 1°, in its lowest form (Medusae), the nervous 

 system is diffuse, and there are no nerve-fibres prop- 

 erly so called; 2°, in a little more advanced stage it 

 tends to form a layer spread out under and parallel 

 wilh the ectoderm; the general histological character 

 is the same as under 1°, — a felted network of fine 

 fibrillae, which spring from the ganglion-cells (Acti- 

 niae, Psuedoneniaton); 3°, the diffuse layer is still 

 present, but certain tracts are more developed, mak- 

 ing the primitive nerve-cords (Chaetognathi, Chiton, 

 etc.); 4°, the diffuse part is gi-adually lost, and the 

 cords are relained. Tliese conclusions are confirmed 

 bv citations from numerous recent researches. Dr. 

 Hubrecht has, we think, successfully established 

 two very important generalizations, — first, that in 

 the lower animals there prevails a uniform type of 

 nervous tissue, ganglion-cell and nerve-fibre being 

 incompletely differentiated, and tlie nerve-fibres being 

 in the form of a network; secondly, that the neiwes 

 were developed by concentration of the diffuse lissue 

 along certain pathways. His paper is certainly one 

 of much value and originality. Systematically the 



position of Pseudonematon is uncertain, but it proba- 

 bly belongs somewhere near the neniatods and plat- 

 helminths. — {Vcrh. acad. wek'iixrh. Aiiwt., xxii. 3d 

 art.) c. s. M. [232 



VERTEBRATES. 



Development of the diaphragm and pericar- 

 dium. — Our knowledge of the changes which lead 

 to the partitioning-off of the anterior end of the 

 body-cavity in vertebrates to form the pericardial and 

 pleural cavities has heretofore remained obscure. 

 Uskow lias investigated the subject under Wal- 

 deyer's direction, at Strassburg, and publishes an 

 important memoir. The essay opens with a review 

 of the previous literature. The research was car- 

 ried out principally on rabbits, but also extended to 

 other mammalia, and classes of vertebrates. At 

 nine days (in rabbit embryos) the omphalo-mesaraic 

 veins enter the body from the sides, along the lower 

 wall of the body-cavity, into which they bulge up. 

 The part of the body-cavity in front is cylindrical; 

 behind, fissure-like. The two cylindrical halves meet 

 anteriorly, and unite below the heart, forming the 

 primitive pericardial division of the coelom. The 

 posterior wall of tliis cavity is pierced by the sinus 

 venosus, and receives the name of septum transver- 

 sum: it is a thin membrane, which separates the 

 pericardial space from the fore-gut of the embryo. 

 In the next stage, the pericardial space has enlarged, 

 the most important effect of which is to drive the 

 septum transversum backwards until it lies together 

 with the omphalo-mesaraic veins, so producing the 

 membrane which supports the great veins, and di- 

 vides off the ventral portion of the pericardial space 

 from the dorsal portion and the general body-cavity, 

 or paired coelom. This membrane then forms part 

 of the wall of the pericardial cavity; but it also 

 forms the primitive diaphragm, the dorsal portion 

 of the original jjericardial space becoming, in con- 

 junction with the anterior end of the coelom, the 

 pleural cavity. 



The pericardial wall consists, according to its devel- 

 opment, of three parts: 1°. part of the original wall 

 of the coelom (this includes that portion which 

 remains permanently attached in mammals to the 

 anterior thoracic wall); 2°. the septum transversum, 

 which becomes the pleuro-pericardiac membrane; 

 3°. the principal part derived from the body-wall, 

 its seimration being consequent upon the enlarge- 

 ment of the pleural cavities. The part from the 

 septum is originally continuous with the diaphragm. 



The diaphragm is at first a connective tissue struc- 

 ture. The muscle grows in later from the dorsal side, 

 appearing first in embryos (rabbits) of nine milli- 

 metres length. It probably is derived from tlie 

 muscle plates, but that was not determined with 

 certainty. The primitive diaphragm arises in its 

 ventral part from a papillary growth of the septum 

 transversum ; in its dorsal i^art, laterally from the 

 tissue carrying the large omphalo-mesaraic veins; 

 medianly, from the outgrowth of the septum trans- 

 versum known as the ma'sa transversa. 



From the comparative study of other types, the fol- 

 lowing grades of develoiimeut of the diaphragm 



