144 CARL BOVALLIUS, AMPHIPODA HYPERIIDEA. I. 2. HYPERIIDvE. 



Hyper ia. 



2. The young ones of species of Hyperia, with two or more perseonal segments coalesced, 

 as far I have had opportunity of observing them, leave the egg with as many pe- 

 rgonal segments coalesced, as the adult animal shows. Thus I have seen young ones 

 of Hyperia Fabrei with the first two perseonal segments coalesced, young ones of H. 

 crucipes with the first three segments coalesced, and lastly young ones of H. tho- 

 racic a with the first five segments thus united. 



3. I have seen and examined ovigerous females and females with newly hatched young 

 ones, enclosed between the ovitectrices, of the following species and with the charac- 

 teristics assigned to them below, Hyperia crucipes, H. thoracic a and H. latissima. 



4. I have examined males of Hyperia Fabrei and H. promontorii with the antennae 

 as well developed as in the adult males of the larger species, H. Latreillei, H. 

 galba and H. spinigera, and the former must thus be regarded as adults, just as 

 much as the latter; (both of the former species had the first two perseonal segments 

 coalesced). 



5. We have homologies, that is to say persisting coalesced perseonal segments, from 

 other Hyperiidean genera as Thaumatops, Phronimopsis, Dairella, Phronima, Phroni- 

 mella and Phrosina. 



6. If this coalescence were only a stage in the growth of the individual it seems very 

 difficult to explain why the sutures between segments so enormously enlarged as 

 those composing the balloon-like peraeon of Mimonectes should not be obliterated and the 

 segments thus be united into a smooth surface as they are in a H}^peria thoracica. 



The glands in the joints of the peraeopoda occur in all the species, but occupy 

 different places in different species and show many peculiarities in the form of the out- 

 lets, these outlets usually occurring on a bulb-like enlargement of the base of the dac- 

 tylus. In some cases the concave side of the dactylus is channelled so as to conduct 

 the secretion to the very tip of the dactylus and thus tranfer it to other places. Sometimes 

 the outlet is covered by a cross-shaped projection from the base of the dactylus, as in Hy- 

 peria crucipes, and sometimes the dactylus is entirely transformed performing the 

 function of a spout. Such transformations occur for instance in the third pair of peraeo- 

 poda of H. latissima and in the seventh pair of H. medusarum and of H. crucipes. 

 These peculiar organs will be discussed in the third or morphological part of this treatise. 



For distinguishing the many species of the genus Hyperia, I have found the follow- 

 ing characteristics to be most useful. 



1. The form of the head, if more or less rounded — or produced downwards into a 

 broad or pointed process. 



2. The perseonal segments, if all free — or some of them coalesced. 



3. The form of the carpus of the first and second pairs of perseopoda, if only a little 

 produced — or much produced. 



