372 LEWIS HENRY GOUGH. 



has relations to sev^enil oocytes at the same time. For all 

 that, ovavial nutritive cell and yolk cell have in common, that 

 both are modified oocytes. The fact that in Avitellina 

 and Stilesia the ovarium has in some degree the double 

 function of ovary and vitelline gland, might be taken as 

 proving the two genera as being primitive. 



The oocytes appear to mature in the ovarium, the reduction 

 of the chromatin taking place before the eggs leave the 

 ovarium. In this Vespect they differ from the oocytes of 

 Tgeuia serrata, studied by Janicki (1907), which mature in 

 the uterus after the penetration of the spermatozoon into the 

 egg-cell. The process of ripening is complicated by the 

 passing of chromatin out of the nucleus into the plasma. 

 Spatlich (1909) observed somewhat similar phenomena in 

 Tetrabothrium before the mitoses take place. For the 

 study of these changes it is necessary to use material that 

 has been stained with iron-h^matoxylin, and to compare 

 with sections stained by other means, as ver^- much depends 

 on the technique of the specimen. Figs. 57-05 show in a 

 series of eggs the most important changes that take place 

 before maturation and immediately after fertilisation. Fig. 

 57 is the youngest stage illustrated ; it represents an oocyte 

 that has already reached its full size. Its plasma shows no 

 modifications whatever, being perfectly homogeneous. A 

 nucleolus is not visible ; the chromatin forms a large round 

 mass. Fig. 58 shows a somewhat older oocyte ; a nucleolus 

 has appeared, and in the plasma two centrosomes can be 

 observed. The centrosomes in the cestode oocyte are quite 

 large objects, as already observed by other authors (e.g. 

 Janicki, 1907). When they first appear they have a light 

 centre surrounded by a dark ring. On the same cell one sees 

 that the chromatin is lying quite on the nuclear membrane, 

 causing it to press out somewhat. Fig*. 59 is also of about the 

 same stage ; in the cell shown a portion of the nucleus 

 appeared to be cutting itself off from the main portion. I 

 cannot say whether this is a regular occurrence or no, as I 

 have only observed it in a single cell. The next changes are 



