■Apkil 27, 1883.] 



SCIENCE. 



345 



placed by Ankylostoma. which has priority for toothed 

 forms of Strongylids. The teeth have been previously 

 overloolved. — (_BuH. soc. zool. France, 1882, 282.) 

 c. s. M. [73 



Insects. 

 Caddis-fly cases. — Miss C. H. Clarke figures 

 and describes two interesting new forms of larval 

 cases of Hydropsychidae from Massacliusetts. One 

 of them, that of a Hydropsyche, resembles a tunnel. 



loosely attached to a stone by its lower edges, the 

 stone forming the bottom. It may be composed en- 

 tirely of sand or of vegetable fragments, or of both, 

 and is peculiar for having at its moutli a vertical 

 framework, with a net stretched across it, as in the 

 figure, to catch its prey. The case is built in swiftly 

 running water, and the supporting framework of the 

 net is occasionally stayed by silken cords stretching 

 to suitable points on the stone. 



The other, that of a Plectrocnemia, is a tall cyclin- 

 drical chimney, with lateral tubes expanding into 

 chambers. The cham- 

 bers usually end with a 

 small apertiu'e, but 

 sometimes extend into 

 another short piece of 

 cylindrical tube with 

 an apertxu'e at its end. 

 The upper end of the 

 main tube has occa- 

 sionally two openings, 

 though commonly one. 

 These tubes are found 

 erect in the muddy bot- 

 toms of brooks, and, but 

 for the apical opening, 

 look like the twigs one 

 may see stranded in 



such places. Miss Clarke was unable to discover in 

 which part of the case the larva lived ; but the pupa 

 was always found in the upright shaft, its place 

 usually indicated by an enlargement. — (Proc. Boat, 

 soc. nat. hist., xxii. 67.) [732 



VERTEBRATES. 



Origin of the vertebrate mesoderm. — Eomiti 

 discusses His's view, that the mesoderm has a double 

 origin, in part from the primitive streak, and in part 

 from independent cells, which His calls parablastic, 

 and thinks derived from the yolk,, and destined to 

 form the connective and vascular tissues. Eomiti 

 admits the double origin, but maintains that the in- 

 dependent cells are derived from the germinal portion. 

 The cells in tlie periphery of the mesoderm are de- 

 rived "from the proliferation of some large cells 

 which have emigrated from the segmented germ, and 

 lie between the primitive layers." — (Arch. ital. biol., 

 ii. 277. ) c. s. M. [733 



Formation of serum albumen in gastric di- 

 gestion. — It is generally believed that proteids, when 

 digested in the stomach or small intestine, are trans- 

 formed into peptones, and absorbed in that form; but 

 there has always been the objection to this view, that 



peptone cannot be found (or, if found, then only in 

 minute quantity) in the blood of the portal vein, 

 or in the chyle.', Hence, if the proteids eaten were 

 turned into peptone, and absorbed in that form, they 

 must very quickly be converted into the albumens 

 of the blood, lymph, or chyle. Von Ott now claims 

 that he has proved that serum albumen is produced 

 in the stomach and intestines during digestion. But 

 his proof consists, 1°, in assuming that Martins was 

 correct when he stated that no proteid but serum 

 albumen will cause the heart of a frog, which has 

 been brought to a standstill by washing with salt 

 solution, to beat again; and, 2°, in showing, that, 

 from the contents of the stomach or intestine of a 

 digesting animal, a solution can be prepared which 

 will make the heart recommence healing. As nu- 

 merous intermediate and by-products are known to 

 be formed during the digestion of albumens, and as 

 Martins did not experiment with several of these, it 

 is clearly necessary that the action of each on the 

 heart be studied before we are justified in concluding 

 that a heart which is fed by a liquid containing them 

 is nourished by serum albumen, and not by them or 

 some one of them. Von Ott finds that milk is an ex- 

 cellent food for the frog's heart, but that it loses this 

 power when all proteids are removed from it. — {-Du 

 Bois' archiv, 18S3, 1.) ii. N. M. [734 



Excitation of vascular nerve-centres by the 

 summation of electrical stimuli. — Kronecker 

 and Nicolaides have examined the influence of suc- 

 cessive stimuli upon the vaso-motor system, in order 

 to see if the vascular nerve-centres obey the laws 

 which have been established in this regard for the 

 reflex movements of the limbs. They find a general 

 agreement. Single induction shocks applied to vaso- 

 motor centres in the medulla or spinal cord have no 

 influence upon arterial pressure. Moderately strong 

 stimuli first begin to act by summation when they 

 follow at not greater intervals than half a second. 

 Increasing the'rate of stimulation increases the effect 

 up to a rate of from twenty to thirty per second: in- 

 crease of rate beyond this has no effect. Keeping 

 the rate quite slow and constant, but increasing tlie 

 intensity of the stimuli, increases the effect, but 

 never so much as quickening the rate. The maxi- 

 mum of blood-pressure can be obtained either with 

 powerful shocks at Tir-i\" intervals, or moderately 

 powerful induction shocks at yd- 2V intervals. It 

 talves longer to attain the maximum result with slow, 

 powerful stimuli, than with weaker, but more rapid; 

 also with slow stimiilation the absolute number 

 whioli must be given before the maximum result is 

 attained is greater. The conclusion is therefore 

 reached, that the cells of the vascular nerve-centres 

 agree essentially witli the proper motor cells of the 

 spinal cord in having an inherent tendency (in the 

 dog) to vibrate at a rate of about twenty times a 

 second. — (CiiBoJs' archiv, 1883,27.) H. N. M. [735 



Tetanic stimulation of frogs' nerves by a con- 

 stant current. — Von Frey has lately carried on a 

 series of investigations as to why a frog's muscle is 

 sometimes tetanised — though usually only giving a 

 single twitch — when a constant galvanic current is 

 sent througli its nerve. He points out some of the 

 conditions under which the long-continued contrac- 

 tion is observed, and shows that it is a true tetanus, 

 and not merely a very prolonged twitch. — [Du Bois' 

 archiv, 1883, 43. ) 11. N. m. [736 



Fisli, 



Spawning-habits of Ceratodus. — Mr. Haswell 

 has stated before the Linnaean society of New South 

 Wales, that Mr. Morton, of the museum, had ascer- 



