584 F. A. Potts, 



visceral mass in the neiglibourliood of tlie longitudinal meseiitery 

 (Fig. H) thus forming a dorsolateral meseiitery, in which the 

 lacuna runs and conveys nourisliment to the visceral mass. This 

 dorsolateral mesentery extends only for a very short space and is 

 succeeded again by a lateroventral mesentery. Posteriorly the visceral 

 mass hangs freely. 



The Structure of the Visceral Mass (PL 16, Fig. 5—7). 



The structure of the visceral mass is extremely simple for it 

 contains only a single organ. the ovary. Externally the visceral 

 mass is enclosed by an irregulär ectodermal epithelium of flattened 

 cells, with a very thin cuticle, succeeded by a thin layer of muscle 

 fibres. The inferior is principally occupied by a cavity, lined by a 

 definite mesodermal epithelium of flattened cells, and into it project 

 a great number of septa formed from the muscles of the above 

 mentioned layer. The epithelial cells clothing the septa send off 

 innumerable protoplasmic bridles to the ovarian follicles 

 occupying the Spaces between the septa. 



The ovary is, in this individual a much shrunken organ owing 

 to the fact that a brood of eggs has been recently laid and the organ 

 has not yet had time to recover. It consists of a large number of 

 follicles each of these being a much twisted and crumpled lamella 

 with a very definite exterual cuticle, The protoplasmic contents of 

 the follicle form a syncytium containing large numbers of small 

 deeply staining nuclei representing the oogonia and also larger 

 nuclei which have aggregated cytoplasm round themselves marking 

 an early stage in the growth of the oocyte. There are not always 

 distinct boundaries between the oocytes but PI. 16 Fig. 7 represents 

 a common condition, several nuclei with their surrounding masses 

 of protoplasm being definitely separated from each other. With their 

 increase in size the nuclei of the oocytes lose their capacity for 

 taking up stains. The same figure illustrates the fact that in each 

 oocyte there are one or two vacuoles. But the cytoplasm is homo- 

 geneous and does not yet contain any yolky constituent. 



The Developing Eggs. 



Eggshaped bodies of a much greater size than the young eggs 

 mentioned above, and with a peculiar and uniform structure occur 

 occasionally in the ovary and very commonly in the ventral part 



