ENTOZOA. 107 



little further on a quantity of very fine granular matter is added, and 

 the cell-nuclei become severally enclosed (eingehiillt) by the fine 

 granular matter, as by a yolk ; around which envelope a cell-membrane 

 is formed. This cell-wall gradually expands ; its inner surface being 

 lined by a layer of granules, whilst in the cavity of the cell the granules 

 have liquified and disappeared. As these changes take place the 

 cell-nucleus becomes developed into an elongate, sharply defined 

 solid corpuscle, which is the spermatozoon. 



The observations recently communicated to the Royal Society by 

 Dr. Nelson * on the development of the spermatozoa in the Ascaris 

 mystax, correspond in the main with Siebold's description. Dr. N. 

 finds the blind end of the testis composed of a thick membrane, 

 which becomes resolved at its inner surface into very minute granules, 

 which, when liberated, swell out into nucleated cells. A little further 

 on these cells are obscured by an immense number of fine granules, 

 which form envelopes for the cells. These cells, which are described 

 to have a very transparent cell-wall and a nucleus attached to one 

 side, answer to the " zellenkerne " of Siebold. According to Dr. 

 Nelson no further development of the spermatozoon goes on in any 

 part of the testis, but is reserved for the transmission of the semen 

 into the uterine tube of the female. Here he describes the sperm-cells 

 as being deprived of their granular envelope and becoming enlarged, 

 forming transparent spheres, with a discoid nucleus which now con- 

 tains a nucleolus. The granular substance of the nucleus increases 

 and projects towards the centre of the cell, and its external layer is 

 converted into a distinct tunic, where it is in contact with the cell- 

 wall, which, as the nuclear matter increases, sometimes pushes out the 

 cell-wall. This, however, does not form the tail-part of the sperma- 

 tozoon in Asc. mystax : the change of the conical to the cylindrical 

 form of the progressively elongating nuclear matter takes place within 

 the sperm-cell, close to its wall. The nucleolus remains in the en- 

 larged or clavate end of the bent cylinder, but the granules disappear, 

 and the nucleus is transformed into a flask-shaped cjecal tubule, which 

 is liberated, as the spermatozoon, by the liquefaction of the surround- 

 ing cell-wall. The nucleolus at the open clavate end of the sperma- 

 tozoon afterwards disappears. 



From the examples which have been adduced of different genera of 

 the Nematoidea, we may perceive that although there are many 

 varieties of structure in the copulative part of the male generative 

 apparatus, the essential or secerning portion uniformly consists of a 

 single tube. A like uniformity of structure does not obtain in the 

 essential parts of the female organs : in a few instances the ovary is 



* XCI. 



