A Coutribut. to the Embryol., Life-history, and Classificat. of the Dicyemids. 65 



In the male Orthonectidae , a single celi is formed at eacli pole of the centrai 

 celi, and these cells multiply subsequently by division , and eventually produce a 

 layer of muscle-fibres that envelop the centrai celi, or its products. Although these 

 cells do not serve as germ-cells, they are ontogenetically coniparable with the 

 priniary germ-cells of the Dicyemids. 



So far then as coucerns the germ-cells of the vermiform embryo, 

 their origiu must be referred to the centrai or axial cell, the nii- 

 cleus ofwhich participates only in the formation of the first two. There 

 is every reason to believe that the infusorific germ-cells bave also a 

 genetic relation with the nucleus of the germogen , although this point 

 has not yet beeu established. 



The account given by Van Beneden with respect to the origin of 

 the vermific germ-cells is a s follows : — «Les germesdes embryons 

 vermiformes se forment par voie endogene. Ils naissent isolé- 

 ment , souvent loin de tout germe préexistant, dans le reticnlura de la 

 cellule axiale. Ils apparaissent sous forme de petits corps sphériques 

 à contour biendéfini. Ils sontdabord homogenes et ils présentent à leur 

 centre un petit globale punctiforme. Le contour devient progressive- 

 ment plus épais : bientot on distingue autour d'un noyau plus clair, nu- 

 cléolé à son centre, une zone peu épaisse d'une substance plus foncée. 

 Cette zone s'epaissit progressivem ent et devient le corps de la cellule- 

 germe.« (l,p.41.) Again on page 43 he says, »Je crois pouvoir aftìrmer 

 que tous les germes , chez les Nématogènes , se forment de cette ma- 

 nière. Jamals on ne trouve de germes en voie de division, si ce n'est 

 ceux qui , arrivés à leur complet développement , se fractionnent pour 

 donner naissance à un embryon. « As before pointed out, Van Beneden 

 maintains the same mode of origiu for the infusorific germ-cells. 



No observations, were made in regard to the formation of germ- 

 cells in the Heterocyemids (2, p. 2031. 



Endogenous Cell-formation. — • The terms »free« and »en- 

 dogenous« bave each been used in two very diff'erent senses : they bave 

 been applied to nuclei and cells which arise w i t h i n other cells, either 

 (1) by division of the nuclei of the parent cells, or (2) independently of 

 pre-existing nuclei, as formations de novo. To avoid ambiguity, it 

 will be well to restrict the use of the word endogenous to cases of 

 the first kind, and to employ, for the second, the word n copiasti e. 



It is a well established fact that cells arise endogenously in a very 

 large number of cases among both plants and animals. The literature 

 on this point has, in part, been noticed elsewhere (51). On the other- 

 hand, the cases in which nuclei, or cells, bave been affirmed to bave a 

 neoplastic origin (»autoplastic«, Lankester, 42) are much less numer- 



Mittheilungen a. d. Zoolog, station zu Neapel. Bd. IV. 5 



