AMPHIPODA. 309 



thoracic limbs. The last jjair is, as in all Isopoda, wanting. In a later stage 

 {Cryptoniscus stage) this missing pair of limbs develops. The larvae of this 

 stage become se.xnally mature as complemental males, protandrous hermaphro- 

 ditism occurring here as in all other Isopoda (Bullau, P. Mayer). At a later 

 stage thej' change into females or into the iinal degenerated male forms (Giard 

 and BoxNiER, No. 167). 



15. Amphipoda. 



Tlie embryos of the Amphipoda, wliich, as has been previously 

 mentioned (p. 148), are distinguished from those of the Isopoda 

 by the ventral curvature of the body within the egg, already have 

 the full number of segments and limbs of the adult. Even the 

 fusions which take place between special segments in some forms 

 are already present in the embryo (F. Moller, !No. 16). Metamor- 

 phosis is consequently reduced to small alterations of shape, increase 

 in number of the joints and olfactory filaments of the antennae, antl 

 additions of setae and teeth. 



A somewhat more jironouuced metamorphosis is found in the Hyperidea. 

 In the newly hatched young of Hyperia, F. Mulleu found no rudiments of 

 pleopoda, whereas Claus, in a Hyperia parasitic on a Discomedusa, found, at 

 a similar stage, the pleopoda and uropoda already developed. As a rule, the 

 young of the Hyperidea, as compared with the adults, in which the eyes are 

 often excessively develo2ied, are remarkable for the smallness of the eyes, and 

 consequently of the head. They are often further distinguished by the shape 

 of the limbs. The young of Fhroaima, for example, have no powerful pincers 

 on the antepenultimate pair of limbs (Pagenstecheu). Spence Bate (No. 2) 

 and more recently Glaus (No. 177) liave published accounts of remarkable 

 differences between the young and the adults, some of which can be referred 

 to the general manner of life. The larvae of Rliahdosoma thus appear remark- 

 ably compact ; tliose of Eidyplds, on the contrary, are long. The Ehahdosoma 

 larva recalls in its structure the genus Vibilia. The abdominal limbs first 

 appear in the form of small rudiments. The Euti/phis larvae resemble in 

 appearance the Gammaridac, so that the deiivation of the Hj'peridea from the 

 Crevettina seems supported by the young stages (Glaus, No. 177). 



16. General Considerations Regarding the Development 



of the Crustacea. 



The study of the metamorphosis of a group so varied and so rich 

 in forms as the Crustacea is one of the most attractive and interestinsj- 

 pursuits for the morphologist. (Jreat importance has repeatedly been 

 attached to individual larval stages from a phylogenetic point of view. 

 Although, in recent times, the NaiqMus and Zoaea have been 

 robbed of their glory as racial forms of the Crustacea, the study of 

 Crustacean metamorphosis does not lose all phylogenetic significance, 

 inasmuch as very distinct indications as to the relationships of the 

 different groups are afforded l^y the manner of their development. 



