386 JOURNAL, BOMB A Y NATURAL HISTORY SOCIETY, Vol. XVIII. 



The homologue of the coelom in Palinurus is to be found in the 

 cavity of the gonads and of the green glands. 



In some of the segmented worms, we find the nephridia utilised 

 for the discharge of the generative products, ova and spermatozoa. 

 It is a characteristic of coelomate animals that both the renal and 

 reproductive organs are derived from the epithelium of the coelom. 



It is therefore not surprising, when we find such distinct evi- 

 dence of serial homology between the gonads and nephridia in the 

 sea worms, to find a certain homology between the green glands and 

 the gonads of Palinurus, such as their cavities representing the coelom 

 and their ducts opening in homologous situations, the basal joints 

 of appendages. 



Development. 

 The female lays an enormous number of coral-colored eggs, pro- 

 bably about a lakh each season. The egg is a single large celi con- 

 tainino- in addition to its nucleus and nucleolus a large amount of 

 yolk granules. After fertilisation by the spermatozoon, segmen- 

 tation commences. In many animals segmentation begins by the 

 complete division of the cell including the yolk into two new cells. 

 This is known as complete division. 



In Palinurus as in most Arthropods segmentation is incomplete. 

 The nucleus divides and subdivides repeatedly till we have a large 

 number of nuclei, the cytoplasm and yolk not being divided up into 

 cells. These nuclei all approach the surface, and later with the 

 protoplasm around them give rise to a germinal layer of cells 

 surrounding the yolk. This central yolk forms a number of cones 

 the base of each being applied to the inner aspect of a germinal cell. 

 The whole embryo is now a hollow bag, formed of a single layer 

 of cells known as the blastoderm (Gr. blaste, a bud, sprout or devel- 

 opment, derma, a skin or layer) its cavity stuffed with nutrient 

 material. 



At one pole of the blastoderm an oval patch, the germinal disc is 

 formed by a thickening of the layer of cells. At one end of the 

 disc a pitting or dimpling takes place and gradually deepens to form 

 a small wide-mouthed pouch. This stage is known as the gastrula, 

 (Latin, a little belly) and may be illustrated by pressing in one pole 

 of a soft tennis ball. 



