waite: antennal glands in homarus americanus. 201 



It seems possible that these ducts may hereafter be shown to repre- 

 sent the ectodermic part of nephridia, while the branchial glands repre- 

 sent the mesodermic portion, in which event the homologs of the entire 

 nephridium would exist in the eleventh and thirteenth segments in 

 Decapods, though the ectodermic and mesodermic portions do not come 

 into conjunction as in Anuelids ; and though, further, the mesodermic 

 constituent is separated into several masses. Such a scheme must 

 remain purely hypothetical until the conditions can be thoroughly 

 studied from the standpoints of both development and comparative 

 anatomy. 



To sum up the foregoing discussions, I believe that there is suffi- 

 ciently good evidence that representatives of the nephridium of Anne- 

 lids are found in Crustacea in the somites bearing the second antenna 

 (antennal gland), the second maxilla (shell gland of Entomostraca and 

 some Malacostraca), and the first maxillipeds (" Segmentalorgan " of 

 Lebedinski) ; and, further, that there is partial evidence of such repre- 

 sentatives in the somites of the first maxilla (Boutchinsky), and in the 

 eight thoracic somites of the maxillipeds and pereiopods of Malacostraca, 

 namely, the branchial glands which exist in all these somites, and the 

 genital ducts which are found in part of them. 



Summary. 



1. The antennal gland consists of three parts : gland proper, vesicle, 

 and duct. 



2. The gland proper consists of endsac (dorsal) and labyrinth (ven- 

 tral), whose lumina are connected by a single small orifice, which is in 

 the lateral anterior part of the organ. 



3. The lumen of the endsac is connected with the exterior only in- 

 directly, by way of the labyrinth. 



4. The labyrinth leads into the duct by a series of converging cana- 

 liculi, which open by separate pores through the dorso-median wall of the 

 duct. These canaliculi form the "white lobe," which projects ventrad 

 from the median anterior region of the labyrinth. 



5. The duct is short and opens through a tubercle on the ventral side 

 of the coxopodite of the second antenna. The opening is guarded by an 

 operculum. 



6. The vesicle is a dorsal diverticulum from the duct, and has no 

 direct connection with the gland proper. 



