224 SUMMABY OF CURRENT RESEARCHES RELATING TO 



the framework is supposed to consist of chromatin. Whether this is a 

 real difference or not remains to be seen. 



(6) " The study of the origin of the pronuclei has an extraordinary 

 importance in this way, that it, as it appears to me, presents the only 

 possibility of following the developmental history of the nucleus. " 



" In regard to the formation of the pronuclei, apart from all the 

 incompleteness of my observations, I consider it possible to demonstrate 

 that the pronuclei arise quite independently of one another, and that the 

 female pronucleus contains only the chromatin of the ovum, and the male 

 pronucleus only that of the spermatozoon." 



Anatomy and Ontogeny of Nematodes.* — Herr N. A. Cobb com- 

 mences with an account of Ascai'is Kukenthalii sp. n., from the stomach 

 of Beluga leucas. The male is from 7-9, and the female 8-10 cm. long ; 

 there are about one hundred caudal papilla, arranged in two irregular 

 rows. Behind the oesophagus there are two delicate organs which con- 

 sist of several hundred tubular elements, connected with one another by 

 fine fibres of connective tissue. The walls of the separate tubes are 

 formed by a layer of epithelial cells, and the tubes contain one to five 

 large vesicular cells, and have an efferent duct ; the several ducts are, 

 at various points, collected into common tubes. Nematodes that live in 

 the stomach of their hosts rarely want these glands, which are absent in 

 such forms as live in the small intestine and the body-cavity ; they may, 

 therefore, be regarded as digestive glands. The ova make their first 

 appearance as nuclei, but soon become surrounded with protoplasm, and 

 finally with a cell-membrane. There are generally three to six masses 

 of chromatin. At a distance of 3 mm. from the blind end of the 

 ovarian tube the ova group themselves round the rachis, and then 

 gradually increase in size. Fertilization and maturation are effected in 

 the seminal pouches, and the upper end of the uterus. Segmentation of 

 the ova, as far as the progastrula stage, is eflected in the uterus. As in 

 all Nematodes yet examined, the first change is equatorial, but in the 

 worm under consideration the two products of division were unequal, the 

 first ectoblastomere being very much smaller than the first endoblasto- 

 mere. The author's results agree pretty closely with those of Gotte and 

 Hallez. 



Seven distinct layers could be made out in the integument ; the 

 cuticle is distinguished by the large quantity of hsematoxylin which it 

 can take up ; the subcuticula is very like the cuticle ; then follow three 

 so-called fibrous layers, each of which appears to consist of parallel 

 fibres united by a connecting membrane. There is a very thin limiting 

 membrane which separates them from the so-called subcutaneous layer, 

 with which the muscle-cells are directly connected. Two kinds of 

 ganglion-cells are distinguished in the central nervous system ; some 

 are large, have a large vesicular nucleus, and give off two or three pro- 

 cesses; others are much smaller and spindle-shaped, and have two 

 processes ; the ganglia formed by them are set close to the nerve-ring, 

 and are connected therewith by nerve-fibres. 



The other new species are Ascaris hulhosa from the stomach of Phoca 

 harbata, Strongylus arcticus from the auditory organ of Beluga leucas ; the 

 anatomy of these new forms is described in some detail. In Oxyuris 



* Jeuaische Zeitschr. f. Naturwiss., xxiii. (1888) pp. 21-76 (3 pis.). 



