No. 2.] THE EMBRYOLOGY OF LIMULUS. 20/ 



Of the coxal glands of the Arachnids we know considerable 

 concerning the adult structure and little about the development. 

 They have been found in Scorpions, Phalangids, Solpugids, 

 Acarina and Araneina. They occur in either somite III or 

 V or they may co-exist in the same individual in two somites 

 at the same time. Usually the external duct becomes closed, 

 as in Limulus, at an early date but in Phalangids (Loman '88) it 

 remains open through life. 



Laurie ('90) describes the development of the coxal gland 

 in Etiscorpiiis italiais. In the youngest stage studied it is a 

 simple straight tube opening distally to the exterior and prox- 

 imally by a funnel to the coelom of somite V, which is a much 

 larger space than in Limulus. ^ In the next stage the duct 

 becomes bent on itself so that it appears in sections cut in 

 three places. Its connection with the coelom is still evident. 

 Later it becomes more complicated and the whole gland 

 becomes enveloped in a thin capsule of mesoderm cells, but the 

 process is not further described. The external opening persists 

 until after hatching. 



Kishinouye ('90) has studied the development of the gland 

 in Agalsena, Lycosa, and other spiders. In these it occurs in 

 somite III and is described as consisting of a duct of ecto- 

 dermal origin which breaks through to the coelom. The 

 schematic figures do not prove this origin of the duct. 



Lebedinsky's account ('92) of the development in Phalangids 

 is most complete. The first appearance of the nephridium is a 

 weak outgrowth of the wall of the coelom of somite III. 

 The cells of this outgrowth become columnar while its external 

 end grows into connection with the ectoderm of the first 

 ambulatory appendage. This thickened portion, which is to 

 form the duct of the organ, now grows inward, carrying the 

 wall of the coelom with it, so that its' internal end is surrounded 

 by a ridge. This inner ingrowth forms the nephrostome. The 

 ectoderm is resorbed later, giving an opening to the exterior, 

 and the tube becomes convoluted. 



1 Kowalevsky and Schulgin {'86) saw the organ when it was but little compli- 

 cated ; they describe its duct as ectodermal. 



