45 



length. The abdomen only lengthens a very little. The 

 elongation takes place during the development of the 

 horns and before the eyes and the other organs disappear. 

 This condition is shown on Plate lY., fig. U ; the nat. 

 size is 11'4 mm. The next phase, represented on Plate 

 IV., fig. 7. shows that the development of the horns, the 

 disappearance of various appendages, and the great 

 lengthening of the genital segment is followed by a loop- 

 ing of the posterior region of the latter. This loop 

 gradually expands, and finally takes on the adult 

 condition. 



In the metamorphosis of the cephalo-thorax the ovaries 

 are thrust into the genital segment, and take up a position 

 on the dorsal aspect of the posterior region of that seg- 

 ment, in such a manner that the more anteriorly placed 

 portion of the ovary in the adult is what was the posterior 

 part in the cyclops stage (see Plate V., figs. 1 and 4). 



The cyclops stage of Lernu^a was first found in situ by 

 Metzger,* who published a short note on the observations 

 made and the conclusions arrived at early in 1868. 

 Clausf later on in the same year, from specimens supplied 

 by Metzger and fresh material, confirmed the observations 

 of that Zoologist. 



Concluding Remark.s. 



In the account set forth on the above pages, it will be 

 seen that there are remarkable differences between the 

 changes that take place in the life history of the two cope- 

 pods before they reach maturity. In the one case 

 {Leijeojyhtheirus) the life history exhibits a series of pro- 

 gressive developments. In the other [Lermea), although 



* Ueber das Mannchen ii. Wcibc-hen der Gattvmg Leincea, vor dum 

 Eintritt der sog. ruckscln'citenden ^Metamorphose. Jany., 1868. 



t Beobachtuiigen ueber Lenueoccru, Peniculus, und Lertioea. 180b. 



