So studies on Arthropoda. I. 



Larvae. — Specimens of Alima, Pseuderichthus and Lvsic- 

 richthus, also the first stage, have been inspected, and the result 

 was always negative. 



IV. Summary. 



The preceding chapter shows that the "dorsal organ" can 

 be observed on the posterior part of the dorsal surface of the 

 head or on the carapace in adults of some or several genera of 

 all orders of Malacostraca, excepting in Cumacea, Tanaidacea 

 and Amphipoda. Whether it sometimes or frequently or even 

 generally has a special function must be made out by a student, 

 who has a good material either of living animals or of specimens 

 especially preserved for histological research, for cutting b>- 

 microtome. As the organ has such wide occurrence, it is no very 

 probable that it has no function in the adult. And this sup- 

 position is strenghtened by the fact that it exists in many and 

 probably in most adult Stomatopoda, but seems to be wanting 

 in their larvae; that it should exist in the embrj^os of this order 

 — on which nothing is known — then be absent in the larvae 

 but reappear in the adults, is highly improbable. We are in 

 reality completely ignorant on the significance of the dorsal 

 organ both in embryos, in larvic and in adults, so ignorant 

 that it seems scarcely possible to produce even a hypothesis. 

 Perhaps experiments on living animals similar to those carried 

 out by some authors in order to investigate the excretor\' 

 system might yield some result. 



