before the so-called Retrograde Metamorphosis. 155 



the males o£ Lerneea, and, indeed, of the Penellinfe in general, 

 so far as I am aware, are not yet known *, and, except the 

 completely transfoniied females, only the first NaujAi us -stage 

 and some, so-called, young forms are described f, the stage of 

 development now to be commmiicatcd, in which in all proha- 

 hilitij copulation takes place^ will not be entirely destitute of 

 interest. 



Mah' form. — Cephalothorax (head and first thoracic seg- 

 ment) longer than broad, exceeding one-third of the whole 

 length of the body, circularly boAved in front, truncated behind. 

 In the middle of the anterior part of the cephalothorax there is a 

 pretty large eye-spot with two spherical lenses. Second, third, 

 and fourth thoracic segments free, gradually diminishing in 

 breadth, and together shorter than the cephalothorax. Genital 

 segment increasing in breadth towards the a])ex, nearly as 

 long as the three free thoracic segments. Caudal piece divided 

 by a slight lateral constriction into two unequal sections, of 

 which the last and largest bears two small processes (furca), 

 each terminating at the apex with three longer bristles. 



First pair of antenna? slender, indistinctly jointed, fringed in 

 front with fine hairs, and terminating with bristles. 



Second pair of antennjfi powerful, three-jointed ; second joint 

 with a tooth-like process, against which the sickle-shaped ter- 

 minal joint strikes. 



In the moveable buccal cone is placed the cylindrical 

 sucking-tube, terminating in a ring armed on its whole cir- 

 cumference Avith an elegant row of little curved teeth ; this is 

 followed by two rings open in front (ventrally), each formed 

 by two semicircular arcs, which appear to be articulated to a 

 band running down to the basal framework of the buccal cone. 

 Externally, on each side of the base of the cone, are the palpi, 

 Avhich bear at their extremity two long and stiff bristles, and, 

 on a lateral basal enlargement, a shorter one. 



The first pair of maxillipedes three -jointed ; basal joint 

 large and Avitli a dentiform process in front on the outer side ; 

 second joint obliquely dilated towards the extremity ; third 

 joint claw -like, slightly curved. The second and third joints 

 together are not very unlike the picture of a pointing hand. 



Second pair of maxillipedes rather stronger, consisting of a 

 large oval basal joint and a long hook-shaped claw-joint. 



First and second pairs of natatory feet biramosc^ the rami 

 two-jointed, last joint Avith long natatory bristles. 



• See Claus, " Ueber die Familie der Lemseen," Wiirzb. naturw. Zeit- 

 schrift, Bd. ii.j). 17. 



t Krover, Naturh. Tidsskr. i. p. 293; and Van Beneden, Recherches 

 £ur la faiine litt. de Bclgiriue (Crustaccs), p. l."30, pi. 10. tip^. o-12. 



