524 
ZOOLOGICAL LITERATURE. 
midae, do not appear to be of essential morphological import. 
This difference is observed before fecundation ; and the author 
thinks it best to regard both as eggs but as different kinds of 
eggs destined for a different evolution, and therefore provided 
with a different stock of nourishment and different protection 
(egg-shell) . The propagation of the Cladocera agrees thus with 
that of the Aphidce in this respect, that in both families there is 
a difference between the eggs which are to be fecundated and 
those which do not require fecundation ; but it differs, inasmuch 
as, in the Cladocera, the same female produces both kinds of eggs, 
which is not the case in the Aphidse. Further, the propagation 
of the Cladocera agrees with that of the Coccidse and Psychidie 
in this respect, that the same female produces both kinds of eggs, 
but differs, inasmuch as in the Coccidae and Psychidae there is 
no difference in the structure of the eggs themselves, but only in 
the circumstance that the one kind requires fecundation and the 
other does not. Therefore the propagation of the Cladocera 
cannot strictly be called either parthenogenesis or alternation of 
generations, but it is an intermediate kind, combining essential 
points of both, and showing that the heterogeneity of the two is 
not so very great as it has been considered by most authors. 
The Danish species of Cladocera are arranged by P. E. 
Muller in the following manner : — 
Fam. I. Daphnidab. Pedes vibratiles, lamellati, obscure ariiculati, val- 
vulis obtecti. 
Subfam. 1. Sidince. Pedes utrinque 6, omnes habitus aequalis, foliacei. 
Ooparum ramus alter 2-3- articulatus, alter 2-3- articulatus aut in 
mare 2-articulatus, in feminis nullus. 
a. Latonttf Sida, Daphnella. 
b. Holopedium. 
Subfam. 2. Daphnince, Pedes utrinque 4-6, habitus imequalis, ex parte 
modo foJiacei. Ooparum ramus alter 3-, alter 4-articulatus. 
a. Daphnia, Shnocephalus, Scapkoleberis, Ceriodaphnia, Moina. 
b. MacrothriXj Drepanothrix , Lathonura^ Bosmina^ Acantholehei'iSy llyo- 
cryptus. 
Subfam. 3. Lyncein<B. Pedes utriuque 6-6, habitus infequalis, ex parte 
modo foliacei. Ooparum ramus uterque 2-articulatus. 
a. Eurycercus. 
b. CamptoeercuSf Acroperus, Alon(ypsis, Alona, Bhrixura^ Pleuroxus^ 
ChydoruSf Monospilus. 
Fam. II. PoLYPHEMiD.®. Pedes prehensiles, subteretes, manifests articu- 
lati, liberi. 
Subfam. 1. Polyphemince. Pedes utrinque 4. Ooparum ramus alter 3-, 
alter 4-articulatus. 
Polyphemus, Bythotrephes, Podon, Evadne. 
Subfam. 2. Lcptodorince, Pedes utrinque 6. Ooparum ramus uterque 
4-articulatus. 
Leptodora. 
