CRUSTACEA 



347 



sphincter of the end sac is perhaps to prevent the passage back into 

 that vesicle, which secretes ammoniacal compounds, of poisonous 

 products excreted in the duct. 



These glands are probably the remaining members of a series of 

 segmental excretory organs. Their mesodermal portions are no doubt 



Fig. 23 1 . Diagrams of the green gland of Astacus. From Parker and Haswell, 

 after Marchal. I, The organ unravelled. II, A section of the organ with the 

 parts in their natural positions, bl. bladder; c.p. cortical (green) portion of 

 the gland ; d. terminal duct; s. end sac; zo.p. medullary (white) portion of the 

 gland. 



coelomoducts, homologous with those of the Annelida, their ecto- 

 dermal portions probably are not the homologues of nephridia but 

 represent ectodermal glands such as are common in the Crustacea. 

 Various other glands, mostly of doubtful morphological significance, 

 which occur in different crustaceans have been shown, or are sus- 



