30 THE DEVELOPMENT OF 



his apparent mistake regarding it. The external opening 

 to the gland is not formed until after hatching. Fig. 74, 

 which passes through the end of the duct, was drawn from 

 a section which escaped the rest of the tube. 



In both of his papers ( '76 and '86) Reichenbach claims that 

 in Astacus the green gland is of ectodermal origin. Be- 

 tween these two dates, Grobben ('79) clearly pointed out 

 Reichenbach's mistake and showed that the gland belonged 

 to the mesodermal tissues. Still, in his later paper ('86), 

 Reichenbach holds to his former opinion. If he were aware 

 of any other view or of Grobben's criticism he does not 

 show it ; for he neither replies to it nor quotes it, but merely 

 repeats his earlier account. I confess it is not easy to rec- 

 oncile Reichenbach's fig. 125 and 126 with my studies of 

 Crangon ; for if the diagrammatic cells and conventional tint- 

 ing are to be trusted, the green gland in Astacus must be 

 derived from the ectoderm, unless the duct form long before 

 the rest of the gland. Ishikawa's observations on the or- 

 igin of the green gland of Atyephyra('85), do not afford a 

 solution of the difficulty ; for although he claims that the 

 gland is ectodermal, his published figures do not conclu- 

 sively settle the question. I have no doubts that the gland 

 in question is mesodermal in Crangon, and that it should 

 be placed in the category of segmental organs or nephridia. 



Sedgwick's recent researches on the embryology of Per- 

 ipatus throw much light on the morphology of the coe- 

 lom and of the nephridia in all of the arthropods, and seem 

 to substantiate Lankester's view that the so-called body 

 cavity of these animals is not homologous with the coelom 

 of the Annelida. According to this view the spaces in the 

 body of an arthropod (blood sinuses, etc.) are all in connec- 

 tion and communication with the circulatory system and 

 must be regarded as portions of a blood vascular room. In 

 Peripatus, on the other hand, the true ccelom has no con- 

 nection with the circulatory system or with the general body 



