xxxviii INTRODUCTION. 



assists in lubricating the branchial plates in warm and 

 strongly evaporating atmospheres. We have been led to 

 this conclusion from finding that they diminish in size in 

 those specimens that have been long detained in dry 

 places 



Generation. 



The organs of generation in the male of the Sessile- 

 eyed Crustacea are not to be determined without great 

 nicety in dissection and care in manipulation. We have, 

 however, in Sulcafor among the Amphipoda, and Ligia 

 among the Isopoda, been able to examine them clearly, 

 besides less perfectly so in the animals of other genera in 

 both orders. Bruzelius and Loven have given their atten- 

 tion to the former order, and demonstrated the arrange- 

 ment in the genera Gammarus and Podocerus. The male 

 organs internally consist of a more or less oblong pair of 

 testes, wliich are liable to vary somewhat in form in 

 different genera. These testes are fitted with numerous 

 small seminal cells. A narrow passage, or vas deferens, 

 connects this organ with a second oval chamber, or 

 vesicula seminalis, which is filled with long fine hair-like 

 spermatozoa, lying thickly coiled one upon another. 

 From the vesicula seminalis a narrow passage leads to the 

 inner surface of the first joint of the seventh pair of legs, 

 where it penetrates in each into a soft membranous 

 external penis. We have kept species of AmpMpoda long 

 under observation, and paid close attention to their habits, 

 but have hitherto failed to detect any communication 

 between the sexes v«'hich would admit of a direct passage 

 of the penis into the vulva of the female. 



The male Ainphidod grasps the female by one of its 

 strong subcheliform gnathopoda, inserting its claw 

 beneath the anterior edoe of the first segment of the 



