600 RECORD OF CURRENT RESEARCHES RELATING TO 



cleavago-plane. The ovum, contrary to Biitsclili and Hertwig, is 

 entered by the siiermatozoon wliile still in the ovarian follicle, not 

 when in the egg-capsule. In the Nematodes fecundation takes place 

 in the oviduct. In Aster acantldon ruhens the directive vesicles 

 emerge from the micropylc. At the ends of the thirty or more thin 

 amoeboid processes of the germinal vesicle aj^pear transitorily stellate 

 figures. The consequences of fertilization may be carried out in sea- 

 water in immature as well as mature eggs. The formation of embryos 

 does not take place if the egg-membrane has not been sufficiently 

 expanded before segmentation. Healthy embryos may be produced 

 from ova into which as many as eight spermatozoa have penetrated. 

 The spermatozoon and the yolk-membrane are connected by a fine 

 process, even before actual contact takes place ; this appears to 

 originate from the former. After the entrance of the spermatozoon a 

 ball of substance appears at the point of entrance ; it originates from 

 the yolk, and swells up to a round bead, larger than a directive 

 vesicle. When sj)ermatozoa enter immature eggs, this swelling has 

 the form of a long stripe, whose end branches out stellately : no 

 segmentation takes place in this case. 



Aulostomum and Hirudo require several years for the genera- 

 tive products to arrive at maturity ; in Nephelis and Clepsine this 

 occurs in the spring of the second year. In them all the sperm- 

 cells penetrate to the ova while these are still enclosed in their 

 follicles ; in Nephelis a ring is formed by them in the middle of the 

 mature part of the ovary. In Nephelis they may enter the yolk and 

 continue to move there ; they also penetrate and remain under the 

 yolk-membrane, but are absorbed when the albumen is developed, 

 as also in Aulostomum, where eight roll about with a screw-like 

 motion in the yolk. In Nephelis the germinal vesicle continues 

 to move after fertilization, sending out two or three stars. The 

 germinal vesicle is visible in Aulostomum when the ovum leaves the 

 ovary ; it then becomes an amphiaster, which is concealed by^dark 

 granules. 



Renal Organs of Invertebrata.* — In the course of an interesting 

 essay on this subject, Dr. Krukenberg gives a valuable table to show 

 the character of the renal excretion, and the organ of the animal in 

 which it was found ; other columns give the authority and biblio- 

 graphical references. We can here only cite some of the more 

 interesting of these. In the AdinicB guanin is found in the mesen- 

 terial filaments (Cams), and the same compound is in Porpita found 

 in a whitish layer on the inferior surface of the mantle (Kolliker). 

 Selenka found no uric acid in the " Cuvierian tubes " of the Holo- 

 thuroida. Bodies closely allied to xanthin or guanin were found by 

 Sommer in the water-vascular system of Tcenia. Uric acid has been 

 detected in some Tunicata. The organs of Bojanus have been 

 frequently seen to contain urea or uric acid. In some Arthropoda 

 similar compounds have been found in the excreta or in the fatty 

 bodies, where green glands and Malpighian vessels are absent. 



* 'Vergl.-Physiul. Stutl.' (Ki-ukenbcrg), ii. (ISSO) p. 14. 



