736 SUMMAnY OF CUURENT RESEARCHES RELATING TO 



New Enchytraeidae.* — Dr. W. Michaclscn continues bis resoarclics 

 on Enchytn\!iJa3. Ho first describes the new genus Stercnlus. The 

 bristles arc S-shapcd ; there is no hcad-porc ; tlie dorsal vessel springs 

 from the girdle segment and is associated with a heart-body ; the blood 

 is colourless ; there are no salivary glands, the gut is adajjted for fluid 

 or semi-fluid nutriment, and is blind ; the vasa dcfercutia are long. 

 S. niveus n. sp. is described in detail, also Pachijdrilus sjjhagnetorum 

 Vcjdowsky, var. uov. glandulosus, Jilcscnchyirseus setosm u. sp. 



^. Nematlielniintlies. 



Fertilization of Ascaris.f — Dr. N. Kultschitzky reports in more 

 detail the results of his investigation of the processes of fertilization iu 

 Ascarls megalocephala. The importance of the subject justifies a fuller 

 summary than was possible from the preliminary communication.! 



He emphasizes the deceptivencss of using ditfereut optical ajipliancea 

 in the observation of these fine details, and rightly insists on the necessity 

 of investigators noting in their researches what objectives, ai)erturcs, 

 &c., they have used. The best fixing medium is an cqnal mixture of 

 alcohol and acetic acid. Acetic ether was also utilized. For studying 

 polar globules and pronuclei fresh material from living animals is 

 essential. For segmentation the dead worm, not later than 3-4 hours 

 after death, must be kept for some hours, or for a stage beyond four for 

 2-3 days, in damp warmth of 35-38^ C. There are several advantages 

 iu inclosing in balsam instead of the usual glycerin. 



The polar globule formation is accomplished after the manner of 

 ordinary karyokinesis. By giving off minute amoeboid processes, tho 

 jirotojjlasm of the sperm is gradually reduced during the formation of 

 the polar globules. Nor is the entire chromatin of the sperm nucleus 

 utilized iu the formation of the male pronucleus. When the second 

 polar globule is extruded, the sperm nucleus has always a distinctly 

 reticular structure. As it is at this stage only rarely quite surrounded 

 by its protoplasm, it is j)artially iu direct contact with the protoplasm 

 of the ovmn. 



In the formation of pronuclei, there is no mixture of male and female 

 chromatin. Both pronuclei arise quite independently of one another. 

 Each consists of a tolerably firm shining achromatic sheath, of a 

 chromatin substance lying apparently in the perij)heral jiortions of tho 

 pronucleus, and forming there a thick network with a number of nodes, 

 of an achromatic substance, and of nucleoli which are usually peripheral. 

 The two pronuclei are quite homologous, they originate in a manner sui 

 generis. The number of pronuclei was sufficiently noted in tho previous 

 summary. 



Each pronucleus begins its karyokinetic changes independently. Tho 

 coil stage, the mother aster, the metakinesis, the dyaster stage, tho 

 daughter coils, and the resting stage are described in detail. The 

 attractive spheres of van Beneden were often observed. They belong to 

 the protoplasm of the egg and represent the first sign of the division of 

 the cell. Kultschitzky calls them " Eichtungssonnen," and is convinced 

 that they belong entirely to the protoplasm. 



• Arch. f. Jilikr. Anat., xxxi. (1S88) pp. 483-98 (1 pi.). 



t Ibid., pp. 567-93 (2 pis.). J Sec this Journal, ante, p. 583. 



