464 TRANSFORMATIONS OF INSECTS. 



were carefully pointed out by the same accurate observer, and 

 then he proved that Praniza had eggs of different shape to the 

 last-mentioned genus. Praniza^ to have eggs, must be an adult 

 form, and therefore could not be the immature zoea of Ancciis. 



Whilst accepting Spence Bate's proofs of the distinctness of the 

 two forms, it must be remarked that M. Hesse had some warrant 

 for his idea that the supposed change from the Praniza stage to 

 that of Anccus took place very late in the life of the creature, 

 for a correspondingly great alteration does occur in other Iso- 

 poda, such as Tanais, the males of which receive a very con- 

 siderable access of abdominal feet simultaneously with the last 

 pair of feet of the thorax, and alter greatly before attaining 

 sexual maturity. 



There are some examples of great retrograde metamorphosis 

 amongst this order of the Crustacea, as a consequence of a parasitic 

 mode of life. The young of the Fish Lice iCymotJiod) are lively 

 swimmers, and the adults stiff, stupid, heavy fellows, whose short, 

 clinging feet are capable of but little movement. Some, which are 

 parasitic upon crabs and lobsters, take up their abode chiefly in the 

 branchial cavity, and then it is found that the adult females are 

 usually quite destitute of eyes. The antennae are rudimentary, 

 the segments of the body are more or less amalgamated with each 

 other, the feet are stunted, and the swimming appendages are 

 transformed into leaf-shaped branchiae. In the males, which are 

 dwarfed, the eyes, antennae, and feet are usually better preserved 

 than in the females ; but, on the other hand, all the appendages 

 and every trace of segmentation have not unfrequently disappeared. 

 In the females oi Entoniscus , which are found in the body cavity of 

 crabs, the eyes, antennae, mouth-organs, the segmentation, and the 

 whole of the limbs (in one species) disappear without leaving a 

 trace. One species would almost be regarded as a flat worm 

 rather than an Isopod, if its eggs and young did not betray its 

 crustacean nature.* 



Metamorphosis appears to be absent in the common wood- 

 louse, which may be taken as the type of the Isopoda. 



The small water fleas, or Daphniidts, are well known to those 



• Fritz Miiller, translated by W. S. Dallas. 



