34 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I3I 



After attachment on the cod the head of the female undergoes a 

 curious transformation. Large branching, hornHke processes grow 

 out from it and sink into the host tissue as anchoring devices (fig. 

 12 I). The proboscisHke mouth region penetrates deeply in the flesh 

 at the base of the gill until a large blood vessel is reached, from which 

 the female will draw a rich nourishment for the maturing of her eggs. 

 The first change of the body is a lengthening of the abdomen, princi- 

 pally the genital segment, which grows out in a twisted wormlike 

 form (G), and finally (H) becomes a long, straight, slender ap- 

 pendage hanging from the thorax. At this stage the female is known 

 as a penella from her resemblance to another adult copepod of that 

 name. In the figure the penella stage shown at H is, of course, drawn 

 on a much smaller scale than is the female at F or G. Next, the abdo- 

 men swells into a great, elongate, twisted bag (I). The female in 

 her final stage is said by Wilson (1917) to attain a length of 40 

 millimeters when fully extended. From now on she is merely an egg- 

 producing organism. Her internal organs (J) consist principally of 

 the enlarged alimentary canal (AlCnl), the ovaries (Ov) and oviducts 

 (Odd), and a pair of cement glands (CmGld) that form the casings 

 for the eggs. The eggs are discharged in two long coiled strings (es), 

 which, Wilson says, reach a lenth of 150 to 200 millimeters. Consider- 

 ing the number of eggs that the species produces, any flounder or cod 

 may consider itself lucky if it escapes infestation. According to 

 Schuurmans-Stekhoven there is only one generation of the parasite 

 each year. 



The metamorphosis of Lernaeocera branchialis affects principally 

 the female on the secondary host. The less modified chalimus instars 

 carry on the developmental processes while attached on the flounder 

 as do the copepodid stages of free-living species. The adult male and 

 the adult female on leaving the flounder are normal, swimming cope- 

 pods. The transformation of the female on the cod involves, on the 

 one hand, a simplification of the thorax until it becomes indistinguish- 

 able from the abdomen, except for the retention of the appendages ; 

 but, on the other hand, there is a new development of anchoring 

 process on the head, and a great overgrowth of the reproductive part 

 of the body. The metamorphosis of the female, therefore, is both 

 recessive and progressive in an anatomcial sense. A study of the de- 

 velopment and metamorphosis should take into consideration not only 

 the anatomical changes that the individual goes through, but also the 

 changes in its instincts. The copepodid of Lernaeocera, for example, 

 must have an instinctive urge to attach itself to a flounder ; the adult 

 female instinctively leaves the flounder and looks for a cod. 



