950 SUMMARY OF CURRENT RESEARCHES RELATING TO 



merely as modifications of the respiratory organs "whicli are found in 

 Peripatus, the Myriopoda, and insects. There has been an adaptation to a, 

 lively mode of life, and, in correlation with the fusion of the segments and 

 contraction of the hind body, a diminution in the number of stigmata. 

 The great development of the skeleton of some has led to a marked localiza- 

 tion of the respiratory apparatus of e. g. scorpions. The Solpugidse present 

 the most primitive relations of the thoracic stigmata, and the Scorpionidae 

 of the abdominal. While it may be supposed that the Tardigrada have lost 

 their respiratory organs, the absence of them in the Pycnogonida must be 

 referred to a primitive condition. Questions as to the homologies of the 

 various stigmata can only be answered after an investigation into their 

 developmental history; the original position of the openings may well be 

 supposed to have been lateral and symmetrical. The diminution in the 

 number of the stigmata has led to an increase of complexity in the trachese 

 connected with those which are persistent. 



e. Crustacea. 



Green Gland of Crayfish.* — Prof. C. Grobben replies to the memoir by 

 Herr B. Rawitz f on the green gland of the crayfish. In that memoir 

 almost all Grobben's previous results were declared by Eawitz to be 

 erroneous. In replying to the criticism Professor Grobben reasserts his 

 original conclusions, and as a comparison of the two reports will show, is 

 in direct conflict with Eawitz on six important points. 



(1) The canal of the green gland does not exhibit any division near its 

 passage into the sac. The terminal sac of the gland passes into the green 

 portion, and that into the white region which expands into the sac. 

 (2) The yellowish-brown terminal portion of the green gland is distinctly 

 a sac with folded walls. (3) Its colour does not depend on a yellow colour 

 of the nuclei, but on yellowish-brown bodies in the protoplasm of the 

 epithelial cells. (4) The cells of the green portion of the gland exhibit 

 towards the lumen of the duct a thick cuticle (Stabchencuticula). (5) The 

 occurrence of strands in the protoplasm of the cells is to be seen in the 

 white portion also, and in fact very distinctly. (6) The terminal sac is 

 richly provided with blood-vessels. 



Embryology of My sis Chamseleo.J — Herr J. Nusbaum commences his 

 account of the embryology of Mysis CJiamseleo with a description of the 

 external changes undergone by the egg in the course of development. 

 Perhaps the most interesting point is that which treats of the blastoderm ; 

 like E. van Beneden, the author finds that the blastoderm appears in the 

 form of a disc, the edges of which grow around the entire egg ; but Herr 

 Nusbaum finds that this disc appears on what will be the ventral surface of 

 the egg. 



The egg is covered by a delicate homogeneous or transparent mem- 

 brane ; the contents are largely composed of the nutrient yolk, formed of 

 more or less large spheres, round grains, and droplets of fat. At what 

 will be the ventral pole of the egg, and just below the membrane, appears 

 a disc formed by a finely granular protoplasm, having in its centre a 

 rounded and slightly elongated nucleus ; the plasma, which is granular at 

 its centre, is converted at the side of the yolk into a homogeneous proto- 

 plasmic layer, which refracts the light strongly. Later on two nuclei are 

 formed by the segmentation of the primitive nucleus. After a lacuna in 



• Arch. f. Mikr. Anat., xxx. (1887) pp. 32B-6. t See this Journal, ante, p. 748. 

 X Arch. Zool. Exper. et Gen., v. (1887) pp. 123-44 (2 pis.). 



