TAPE- WORMS OF THE SUB-FAMILY AYITELLINIXJ-:. 371 



not contain very many eggs ; an ovarium produces at tlie most 

 fifty to one hundred eggs, a lobe probably not more than one 

 dozen. Besides the eggs, each ovarium contains a number 

 of smaller cells, probably abortive oocytes, which lie scattered 

 between the eggs and along the walls of the lobes. Fig. 42 

 represents a single such cell lying between three oocytes, 

 which have not been completely drawn. For these cells I 

 propose the name ovarial nutritive cells, on account of their 

 probable function. They are much smaller than the oocytes, 

 and are fairly rich in plasma. In shape they accommodate 

 themselves to the space at their disposal between the eggs. 

 They are very extensively in contact with the eggs, sending 

 out plasmatic processes along and over the surface of the 

 surrounding oocytes. Their nuclei are oblong, rather pale, 

 especially as compai-ed to those of the oocytes, and contain a 

 varying number of small round chromatin bodies. The 

 diameter of a nucleus averages 17 ju by 9 fx. 



There seems to me to be no possible doubt about the 

 function of these cells. They act vicariously for the missing 

 yolk-cells, and supply the oocytes with nutriment by means 

 of the processes touching and covering their surface. Ac- 

 cording to the accepted theory, the yolk-glaiid (vitelline 

 gland) is only a modified ovarium, and the yolk-cells modified 

 oocytes. Should this theory be correct, it would render the 

 mutation of oocytes into nutritive cells within the ovarium 

 easy to imagine, the chief difference from the state of things 

 existing elsewhere being-, that here both nutritive cell and 

 oocyte arise in the one ovary, elsewhere the oocytes arise in 

 the ovary and the nutritive cells (yolk-cells) in a modified 

 ovary, the yolk-gland. A very important difference, however, 

 still remains. The yolk-cell of other cestodes becomes attached 

 to the oocyte, and remains closely united to it for a long 

 period after having handed over to the oocyte its supply of 

 yolk, being enclosed in the shell with the oocyte. In 

 Avitellina and Stile si a the nutritive cell is only tem- 

 porarily connected with the oocyte, it does not leave the 

 ovarium when the oocyte does, and finally one nutritive cell 



