42G SUMMARY OF CURRENT RESEARCHES RELATING TO 



" classic." The species which Boveri studied were Ascaris megalocephala 

 and A. lumbricoide8. 



(1) The author has shown, and the ohservation is very welcome, that 

 two types of ovum exist, one (van Beneden's type) with a single chro- 

 matic clement, the other (Carney's type) with two. 



(2) He is also convinced that the separation of the two polar globules 

 in both the species investigated is a true mitotic division, and no pseudo- 

 karyokinesis as van Benedcn would have it. 



(3) His main conclusions are as follows : — (a) the daughter ele- 

 ments shift to the poles of the directive figure, and true daughter plates 

 arise ; (b) the spindle is lessened before division, but does not disappear; 

 (c) the chromatic elements are halved in the formation of each polar 

 globule ; (d) in each of the two polar globules there are exactly as many 

 elements as are present in the ovum at the moment of the formation ; 

 (e) of each of the elements half goes to the first polar globule, and the 

 elements are again halved to form the second body ; the female nucleus 

 contains as many elements as the germinal vesicle, though each is 

 reduced to a quarter of its original volume ; (/) the fibres between the 

 daughter plates are not independent of the old figure, but are indeed the 

 same as the " connecting fibres " of the karyokinesis. 



Life-history of Ascaris lumbricoides and Taenia elliptica.*— -Dr. 

 A. Lutz brings forward some evidence in favour of the view of Grassi that 

 these parasites may continue to exist without the intermediation of a 

 second host. Prof. Leuckart | fully recognizes the lacunar condition of 

 our helminthological knowledge, but does not think that there is yet 

 sufficient evidence to justify us in regarding as incorrect conclusions 

 which are founded on positive facts. 



y. Platyhelminthes. 



Development of Generative Organs of Cestoda4 — Herr F. Schmidt 

 comes to the conclusion that the whole of the generative apparatus of 

 Tapeworms, inclusive of the efferent ducts and genital passages, arises 

 from elements of the parenchyma ; or, in other words, from elements of 

 the parenchyma of the young proglottids which is characterized as tissue 

 of an embryonic character. The organs are not developed from one 

 rudiment, nor are they to be referred to a definite group of cells ; they 

 appear as quite independent rudiments in the parenchyma and in 

 positions which correspond generally to the position of the fully de- 

 veloped organs. The yolk-glauds of Bothrtocephalus and Trisenojihorns 

 arise quite independently of the primary generative rudiment, for their 

 elements are at first scattered in the parenchyma of the cortical layer 

 at a time when the primary generative rudiments have not undergone 

 much differentiation, and before the efferent ducts have been de- 

 veloped. In a good series of sections it is easy to show that the 

 testicular vesicles are likewise independently developed in the paren- 

 chyma of the median layer. These observations doubtless apply to 

 other Cestodes. The so-called primary generative rudiment is not a 

 sharply limited structure, which can be easily distinguished from the 

 surrounding parenchyma ; it does not become distinct when the different 

 organs begin to be differentiated ; it grows by the constant proliferation of 



* Centralbl. f. Bakteriol. u. Parasitenk., i. (1887) pp. 713-8. 



t Loc. cit., pp. 718-22. % Zeitschr. f. Wiss. Zool., xlvi. (1888) pp .151-87 (2 pis.)- 



