M . E. Hesse on the Pranizae and Ancei. 413 



second pair of footjaws, also composed of four joints, of which 

 the apical one is the narrowest ; these, which, like the preceding, 

 are in a vertical position, close the buccal orifice. 



The head, in the transformation of the females into Ancei, is 

 the last part to undergo metamorphosis ; the author has seen 

 individuals in which the whole body had become changed, whilst 

 the head still retained its Praniza-ioxm. 



The lower surface of the thorax is covered throughout with 

 large oval laminae, which spring from the outer margin and join 

 in the median line ; these form a large incubatory pouch, in 

 which the ova and young are contained. 



On the Habits of the Ancei. 



The fecundation of. the females is effected while they are still 

 in the Praniza-statc. Immediately afterwards they become 

 transformed into Ancei, and the ova make their appearance ; 

 but, as in many other Crustacea, the young do not at once quit 

 their mother, but remain attached beneath her thorax, probably 

 waiting until she shall transport them into situations where 

 they will be able to find their proper nourishment. In a few 

 days, however, they disperse, swimming with great rapidity. 



After the exclusion of the young, the female appears quite 

 empty and reduced almost to a mere skin ; but through this the 

 digestive apparatus, still containing some food, may be detected : 

 in this condition their movements are very slow, and they soon 

 perish. The existence of the males, on the contrary, may be 

 much more prolonged : the author has kept one of them alive 

 for two years, although it was placed in unfavourable circum- 

 stances. The Praniza, also, may live for a long time : some of 

 them were kept for two years before undergoing their trans- 

 formation into Ancei. Their vitality appears to be extraordinary. 

 In examining them under the microscope, M. Hesse, in order to 

 paralyze their movements, immersed them in fresh water, and 

 even mi.xed this with alcohol, and kept them in this fiuid until 

 all motion, and even circulation, was suspended ; but neverthe- 

 less, by putting them again into sea-water, he found them alive 

 and active on the following day. 



The reproduction of the Ancei appears to take place at all 

 seasons, young animals of various ages being always found mixed 

 with the adults. Nevertheless the author thinks that fecunda- 

 tion takes place in September, October, and November. 



All the individuals found upon fishes were in the Praniza- 

 form, and these speedily became transformed into Ancei ; those 

 obtained on the shore, and mixed with Ancei, rarely underwent 

 this metamorphosis. The Praniza inhabit the interior of the 

 mouth of fishes, fixing themselves upon the palfite and the 



