402 SUMMARY OF CURRENT RKSEARCHES RELATING TO 



germiual layers — the ectoderm (which form stomodseum and procto- 

 dgeum) and the secondary endoderm (which originates from the primary 

 endoderm or lower layer, and forms the small and relatively unimportant 

 mesenteron). 



Gastrulation in two stages occurs in many types of animals besides 

 Arthropods, and seems connected with abundant yolk. In the first phase 

 yolk-endoderm is formed which works on the yolk, but does not usually 

 share in making the embryo. In the second phase the gastral endoderm 

 is formed, and gives rise mainly to the enteric epithelium, it may be to 

 the mesoderm as well. There is never a total degeneration of endoderm 

 such as Heymons believes to occur in Pterygota. 



Minute Structure of Sensory System of Dragonfly Larvae.* — A. 

 Zawarzin has made a histological study of the sensory nervous system 

 of the larvae of various species of JEsclma. The sensory organs, in 

 addition to the eyes, are referable to three groups— tactile setae with 

 nerve-endings at their base ; organs of taste or chemical sense, such as 

 the cones of the antennae and maxillary palps, with the ends of the peri- 

 pheral processes of the innervating cells brought as near the exterior 

 as pjssible ; and, thirdly, the chord otonal organs in the trochanters 

 and tibiae of all the legs. The author has discovered a very complex 

 " Jonston's organ " in j^schna larvas. 



The peripheral sensory nervous system consists chiefly of bipolar cells, 

 one for each sensory structure, except in the case of the taste-organs of 

 the labrum, which are innervated by a group. From the spindle-shaped 

 cells an unbranched process passes to the sensory structure, and an un- 

 branched but varicose process to the central system. There is a second 

 kind of cell, with an arborescent peripheral process and a central process 

 as in the other kind. These cells occur at definite places in definite 

 numbers. 



Muscle Degeneration. t — Ivar Thulin has studied the degenerative 

 process in a paralysed dragonfly {Libellula). The fibres show a pale- 

 scence of transverse disks and granules. The granules become swollen 

 and show fatty degeneration. The sarcostyles show a structure like that 

 of the disks, probably indicating a fatty modification. A blue-coloured 

 body of diverse shape appears in the granules ; the cross-striping dis- 

 appears and the granules become paler and paler : they become mingled 

 with the degeneration-products of the endoplasm, especially of the nuclei. 

 The muscle of the wing becomes a mass of detritus. 



Structure of Alimentary Canal of Stick Insect.* — A. E. Cameron 

 has studied the gut of Barillus rossi. It has no convolutions and no 

 gizzard. There are very rudimentary digestive caeca and there are small 

 tubular appendages of the mid-gut with filiform ends. The anterior 

 portion of the mid-gut is puckered owing to the isolation of the circular 

 muscle-bundles. The Malpighian tubes are curiously grouped in bundles 

 of from three to six, each bundle opening into the gut by a common duct. 

 The small intestine is separated from the rectum by six powerful pyra- 



* Zeitschr. wiss. ZooL, c. (1912) pp. 245-86 (3 pis. and 9 figs.). 

 t Arch. Mikr. Anat., Ixxix. (1911) pp. 206-22 (1 pi.). 

 + Proc. Zool. Soc. London (1912) pp. 172-82 (3 pis.). 



