INDUSTRIAL PKOGRESS DURING THE YEAR 187G. cliii 



Van Beneden claims that they have no general body-cavity. The 

 body is formed (1) of a large axial, cylindrical, or fusiform cell, which 

 extends from the anterior extremity of the body, enlarged into a 

 head, to the caudal extremity ; (2) of a single row of flat cells, form- 

 ing around the axial cell a sort of simple pavement epithelium. All 

 these cells are placed in juxtaposition like the constituent elements 

 of a vegetable tissue. There is no trace of a homogeneous layer, of 

 connective tissue, of muscular fibre, of nervous elements, nor of inter- 

 cellular substance. There is only between the cells a homogeneous 

 {imissante) substance, as between epithelial cells. The axial cell is 

 regarded as homologous with the endoderm of the higher animals 

 {Metazoa). He designates as the ectodermic layer the cells surround- 

 ing the large single axial cell. There exists no trace of a middle 

 layer of cells. We discover no diflerentiated apparatus ; all the an- 

 imal and vegetative functions are accomplished by the activity of 

 the ectodermic cells and of the axial cell. On account of these char- 

 acteristics, Van Beneden regards these organisms as forming the type 

 of a new branch of the animal kingdom, which he designates Me- 

 sozoa. 



Each species of Dicyema comprises two sorts of individuals differ- 

 ing externally, one (the Nematogene) producing vermiform embryos, 

 the other (Rhombogene) infusoriform young. The Nematogenes pro- 

 duce germs which undergo total segmentation assume a gastrida 

 condition. After the closure of the blastopore the body elongates, 

 the worm-like form of the adult is finally attained, and they pass 

 through the body-walls of the parent. 



The germs of the Rhombogenes arise endogenously in special cells 

 lodged in the axial cell, and called " germigenes." The germ-cells 

 undergo segmentation, and then form small spheres which become 

 infusoriform embryos. The worm-like young is destined to be de- 

 veloped, and live in the cephalopod where it has been born, while 

 the infusorian-like young jDrobably performs the office of dissemi- 

 nating the species ; it transmits the parasite of one cephalopod to 

 another. 



This work is also an important contribution to histology, particu- 

 larly to the subject of cell-divisions. Says Van Beneden : " The re- 

 cent researches of Auerbach, of Blitschli, of Strasburger, of Hert- 

 wich, and those that I have published, have established the fact that 

 the division of a cellule that is to say, the multiplication of the 

 cellular individuality is the resultant of a long series of comjjlex 

 phenomena, accomplished in a determinate order, and having their 

 seat as much in the nucleus as in the substance of the cell." 



Finally, Van Beneden places in his branch of Mesozoa the hypothet- 

 ical Gastrceades^ which term he applies to {gastrida-Vike?) organisms 

 formed of two kinds of cellules, some ectodermic, others endodermic, 

 m which the endoderm is formed by invagination. He calls Plunu- 



