180 



SCIENCE. 



[Vol. I., No. 6. 



of the twigs become their winter habitat. The arbor- 

 vitae, and small trees with many slender branches, 

 are their favorite resorts, and, when once attacked, are 

 frequently destroyed. After the basket is well con- 

 structed, they have few enemies; but so persistent are 

 these few that they nearly exterminate the basket- 

 worm. At least seventy-five per cent are annually 

 consumed by very small ichneumon flies, about one- 

 eighth of an inch in length. Only about five per cent 

 of those opened had ovaries filled with eggs. 



Most of the T. ephemeraeformis thus infested with 

 parasites are pupae; but some are found in the imago 

 state, when the eggs have become the favorite food, 

 and are wholly consumed. 



There is only one brood annually ; and, from what 

 has been observed, it is quite evident that all shrubs 

 and trees may be ridded of these pests by picking the 

 cases off during the winter or early spring. — ( Tren- 

 ton nat. hist. soc. ; meeting Feb. 13. ) [391 



Fertile eggs from a dead moth. — Mr. F. G. 

 Schaupp states that last July he captured a S of 

 Arctia vii-go, and obtained about a dozen eggs. As 

 tbe specimen was useless for the cabinet, having lost 

 half a wing, he dissected the abdomen, and found 

 about fifty eggs therein, sticking together. After 

 washing them with tepid water, he put them in a 

 hatching-box, and in due time about twenty young 

 larvae made their appearance. Could the same thing 

 not be done when capturing a poor 9 of a rare 

 species? — (Brookl. ent. soc. ; meeting Feb. 3.) [392 



VERTEBRATES. 



Relation of spinal-cord nerve-cells to fibres 

 in the spinal nerves. — A careful enumeration of 

 the large ' motor cells ' in the anterior cornua of the 

 spinal cord of the frog, and of the number of nerve- 

 fibres in the anterior and posterior roots of the spinal 

 nerves, has been made by Birge. He finds that there 

 are just as many motor cells in the cord as fibres in 

 the anterior roots, and that in regions where the fibres 

 joining the cord are numerous, the motor cells are 

 proportionately increased in number. When an in- 

 dividual shows some abnormality in the distribution 

 of nerve-fibres between its anterior roots, a corre- 

 sponding irregularity is found in the cells of the an- 

 terior cornua. It is therefore almost certain, that 

 each motor nerve-fibre has its own single nerve-cell 

 as its central organ, and that these cells lie in the 

 spinal cord near the level at which their fibres join 

 it. As the frog grows, the number of nerve-cells in 

 the anterior horns of the gray matter, and the number 

 of fibres in the anterior spinal roots, increases, proving 

 a continued development of motor cells and motor 

 fibres as the muscles increase in mass. 



In any given specimen the fibres in the sensory 

 roots are more numerous than those in the motor. 

 The sum of the fibres in the anterior and posterior 

 roots of a spinal nerve is equal to the number of 

 fibres in the common trunk formed by their union 

 beyond the ganglion of the posterior root. Hence, in 

 traversing its ganglion, the sensory root experiences 

 no increase or diminution in the number of its nerve- 

 fibres. — (DMi«oisVlrf/«i)., 1882,435.) ii.n.M. [393 



Irritability of motor-nerve cells in the spinal 

 cord. — If parts of the spinal cord of the frog be 

 cut or pricked, tetanus occurs in certain groups of 

 muscles. Such tetanus does not follow cutting or 

 pricking a nerve-trunk. Working with special appa- 

 ratus, and M'ith methods making it possible to as- 

 certain exactly what part of the spinal cord was 

 pricked, Birge finds that in the region of the spinal 

 cord from which the sciatic plexus originates, the 

 insertion of a needle-point only causes tetanus (with 



rare exceptions) when the needle has passed through 

 the region of the gray matter in which the motor 

 cells lie. Pricking the gray matter elsewhere has no 

 effect on the muscles, or only causes a ' twitch ' in- 

 stead of a tetanic contraction. He concludes that the 

 motor cells are capable of direct mechanical stimu- 

 lation, and that a momentary stimulus throws them 

 into a state of activity which lasts longer than the 

 application of the stimulus. As his pirevious work 

 (see 393) had made it pretty certain that each motor 

 fibre ended in one definite motor spinal-cord nerve- 

 cell, he concludes that any normal stimulus (volun- 

 tary or reflex), acting in tlie ordinary working of the 

 body on the motor cells of the spinal cord, will, no 

 matter how transient it may be, cause, not a twitch, 

 but a tetanic muscular contraction of longer or 

 shorter duration. — (DuBois' Archiv., 1882, 481.) 

 H. N. M. [394 



Influence of respiratory movements on ar- 

 terial pressure. — In a previous work Schweinberg 

 had shown that in dogs the normal respiratory varia- 

 tions of arterial pressure disappeared upon cutting 

 the phi-enics. He concluded that the variations were 

 due to changes of intra-abdominal pressure, depend- 

 ent on diaphragmatic contractions and relaxations. 

 If this be so, the respiratory curves of arterial press- 

 ure ought to disappear even with intact pbrenics, if 

 all circulation through tlie abdominal arteries be pre- 

 vented : this Schweinberg finds to be the case. When 

 the thoracic aorta is tied above the diaphragm through 

 an opening made in the back of the thorax with 

 care to leave the pleurae intact, then, unless the 

 breathing becomes forced and abnormal, all the res- 

 piratory variations of arterial pressure cease. — 

 (xtrc/i. /ii}-p/i2/sJo!., 1882, 540.) ii. N. M. [395 



The fatigue curve of striated muscle. — A 

 short paper on this subject by Valentin contains as 

 its chief novelty the fact that repeated feeble exer- 

 cises of functional activity by a frog's muscle through 

 which no blood is circulating aid in restoring the 

 fatigued organ, so that subsequent contractions be- 

 come more powerful. — (Pfliirj. arch., xxix. 506.) 

 H. N. M. [396 



Birds. 



Germinal disk of birds. — Gasser has published 

 an article containing several matters of interest. He 

 first supplements his previous observations on the 

 neurenteric canal, and reviews Kupffer's work. He 

 still maintains that in birds "the primitive groove 

 first becomes distinct on the anterior part of the primi- 

 tive streak, and there becomes deepest; this deepest 

 part corresponds to the spot where in many bird em- 

 bryos the perforation of tbe neurenteric canal subse- 

 quently occurs. " He then passes to the consideration 

 of Roller's investigations, whose conclusion is, that the 

 primitive streak is normally preceded by a ^ sicheV 

 (a crescent-shaped thickening of the inner germ layer 

 on the edge of the area pellucida). On the contrary, 

 Gasser maintains that the 'randwulst ' is thicker 

 behind than in front, and the thickened portion may 

 present sometimes in surface views the figure of a 

 crescent, and that a sichel as a structure distinct 

 from the randwulst is not proved by Koller to exist. 

 Further Gasser argues against Koller's assertion that 

 the primitive streak grows forward out of the sup- 

 posed sichel ; and he declines to admit any morphologi- 

 cal importance for the groove, which is occasionally 

 found in the randwulst (Koller's sichel), and upon 

 which Koller lays such stress. Next follows a brief 

 notice of Balfour and Deighton's paper. The remain- 

 der of the article is occupied by the author's own 

 recent investigations on the chick, goose, and dove, 



