306 APPENDIX IV 



having a muddy look, doubtless due to the excretory matter 

 absorbed. How this matter is discharged we cannot see. 

 The cuticle is extremely thin and perhaps allows of passage 

 through it. If so, what is the use of the single fine pore at 

 one end, which by itself could apparently only relieve one or 

 two of the hypodermis cells ? We have thus not been able 

 to ascertain the mechanism of discharge, but that the whole 

 organ is essentially glandular, no one who has studied it can 

 doubt. 



We can say nothing certain as to the origin of this organ. 

 From its relatively enormous size in the Nauplius, 1 it 

 is clearly the principal larval excretory organ, and under- 

 takes the discharge of waste products before the shell gland 

 appears. It may perhaps be a sort of island of Annelidan 

 hypodermal glandular cells left by the developing exo- 

 skeleton, taking the place of the head nephridia of the 

 Annelidan larva. That these latter should not be developed, 

 owing to the bending double of the front segments of the 

 Crustacean-Annelid, was to be expected. We may perhaps 

 therefore find in this neck organ a group of dermal glandular 

 cells, derived from the Annelidan dermal glands, and 

 serving for excretion until the typical Crustacean glands 

 are developed. Its singular position in the larva may 

 perhaps be considered as protective, since an excretory 

 gland might well serve as a protective organ on the exposed 

 dorso-frontal surface. 



A comparative study of this organ, which also plays an 

 important part as an excretory organ in most Crustacean 

 embryos or larvae, is much to be desired. According to 

 Bullar, in some Isopodan embryos it forms as an invagina- 



1 In the Nauplius, figured p. 1 60, it measures about 0.25 mm., whereas 

 that of the adult L. productus (Fig. 69) measures only 0.5 mm. 

 Brauer, curiously enough, shows no traces of it in the Nauplius of L. 

 productus (Fig. 35). 



