568 SUMMAKY OF CUBBENT BESEABCHES BELATING TO 



ably to a study of the successive phases in the development of the 

 spermatozoa, not only on account of the comparatively large size of the 

 spermatozoa, but also because of the simple and typical arrangement 

 of the male apparatus, which is formed by a single tube whose 

 diameter insensibly increases in size from the blind end to the orifice. 

 The best method of investigation is to use the double means of first 

 examining successively dissected portions of the seminal tube, and of 

 making a series of sections of a tube first hardened and properly 

 stained. If we wish to avoid the errors into which preceding 

 writers have fallen, we must be very careful to neglect no part of the 

 tube. The later authors, such as Schneider, Nussbaum, and Hallez 

 have, further, committed the fault of neglecting the bibliography of 

 the question, and especially the excellent work of Munk published as 

 long ago as 1858. 



The authors proceed to a description of the several parts of the 

 male tube — testicle, efferent canal, seminal vesicle, and ejaculatory 

 canal. They describe then in detail and sum up their results in the 

 following terms : 



It is necessary, in the history of spermatogenesis, to carefully 

 distinguish between the formation of the spermatogonia at the 

 expense of the spermatomeres, and the division of spermatogonia into 

 spermatocytes. The multiplication of spermatogonia appears to be 

 effected, in A. megalocephala, directly and not by karyokinesis, 

 while the spermatocytes arise by the indirect or karyokinetic division 

 of the spermatogonia. The karyokinesis presents some special 

 characters ; the typical form of the chromatic cord is replaced by a 

 rod-shaped form, and the primary loops have the shape of truncated 

 cones. The longitudinal division of the primary loops results from 

 the appearance of a circular vacuole in each of the pyramids ; this 

 vacuole extends to the equatorial plane, and brings about the division 

 of the pyramid into two quadrilateral plates, which represent the 

 secondary loops. The polar corpuscles which occupy the centre of the 

 attractive spheres are remarkable for their affinity for colouring matter. 

 The asters may be distinctly seen to be the cause of the temporary 

 division of the cell into three portions, separated by circular con- 

 strictions. 



In the region where the spermatogonia are formed at the expense 

 of the spermatomeres there are to be observed, between the cells, 

 corpuscles which have a close resemblance to polar globules ; these the 

 authors call residual globules. They appear to have been expelled 

 by the spermatomeres after the karyokinetic metamorphosis, and the 

 expulsion seems to be effected in the equatorial plane of the dicentric 

 figure, as in the case of the polar globules. If this account be 

 correct, the residual corpuscles are comparable to the polar globules 

 of the egg. 



The spermatocyte, before becoming a spermatozoon, gives off a 

 portion of its substance, which belongs to the cytophoral part ; the 

 formation of the cytophore is in no way comparable to a cell-division. 

 Just as the egg, when completely matured, is a cell reduced to that 

 which Van Beneden has called a female gonocyte, so is the spermatozoon 



