44 SUMMARY OF CURRENT RESEARCHES RELATING TO 



of spherules, and the appearance of two separate spindle figures. At 

 the very first there is dualism, each half contains an equal number of 

 chromatin rods ; the dualism is still preserved in the formation of the 

 two polar bodies ; a double fertilization also occurs ; each of the chro- 

 matin portions unites with half of the sperm chromatin ; two segmenta- 

 tion nuclei are formed, which have, however, a single functional import, 

 since each furnishes at the beginning of segmentation two chromatin coils 

 for the single mother-star of tho first segmentation. The two segmentation 

 nuclei have been wholly misunderstood, and erroneously interpreted as 

 pronuclei. 



The germinal spot or so-called nucleolus includes all the formed 

 chromatin substance of the ovum, it is rather comparable to a nucleus, 

 it is a structure sui generis, and to it, as to the similar body in the sperm, 

 the designation mitoblast may be applied. 



Prof. Zacharias then describes the male elements, noting the 

 successive changes, the amoeboid and the passive portion, the important 

 naked mitoblast which does not deserve the name of nucleus, denying 

 that the sperm and ovum are, as Nussbaum says, homologous, while 

 acknowledging that they are complementary cells. He takes a brief 

 survey of incipient dimorphism of sexual elements, and maintains the 

 fundamental physiological and histological differences between ovum and 

 sperm. 



II. The Conjugation of the Sex-cells. — "While in the main corro- 

 borating the classic results of Van Beneden, the author differs from him 

 in sundry details, especially as regards the mode in which the sperm 

 penetrates the ovum. He finds, for instance, no micropyle. The egg 

 substance never forms a naked protrusion to serve as the attaching point 

 for the spermatozoon. The penetration of the sperm begins with the 

 emission of pseudopodia, but the rest of its progress appears to be passive. 

 By some local regeneration, the membrane closes upon the entrant sperm. 

 The sperm has in itself power to penetrate the membrane. In regard to 

 the point where the sperm may enter, Zacharias observed that in the 

 elliptical ova of A. suilla, the male elements were seen fixed both at the 

 pole, and on the sides. Polyspermy occasionally occurs, but is to all 

 appearance pathological. It may be that the ovum, being amoeboid and 

 exhibiting contractions, may form a small cone of attraction into which 

 one sperm normally finds its way. The membrane thickens after the 

 entrance of one sperm. Some notes on the genital ducts are then 

 made. 



III. Formation and expulsion of Polar Bodies. — The double structure 

 which results from the originally single germinal vesicle, has been already 

 noticed. The two half-spindles occupy various relative positions. The 

 ypsiliform figure so familiar in Van Beneden's researches is only a 

 special, and not a typical form of spindle. The division forming the 

 polar bodies takes place radially, and not tangentially to the surface of 

 the yolk, the difference on which Van Beneden lays so much stress does 

 not occur in properly killed and fixed ova. The extrusion of the second 

 body is also normal in its karyokinesis. In the first extrusion the 

 original number of chromatic elements is halved and thus reduced to 

 four, in the second process half is again given off, so that three-fourths 

 of the female chromatin is excluded from share in the embryonic 

 development. At the time of the second polar body formation, the 

 dualism of the male element is well marked. This chapter closes with 



