426 Dr. H. J. Hansen on the MorpJiology of the 



with this the plate situated upon the outer side of this same 

 first segment in Branchipus and Cladocera (§9), which 

 probably subserves the purpose of respiration. In the same 

 manner we may also explain the presence of the branchiae 

 arising from the body at the base of the limb in Lophogaster^ 

 Gnathophausia, and Eucopla. 



25. According to §§22 and 18 the exopodite of the maxil- 

 lulffi and maxillffi, if it is present at all, always proceeds from 

 the third segment in the case of the orders mentioned; it 

 therefore follows that in these two pairs of oral appendages 

 the primitive number of segments in the stem of the appen- 

 dages is preserved and that the first segment comes to belong 

 to the same category as the mandible, but not the coxopodite 

 of the limbs. 



26. The Leptostraca are decidedly the lowest of the Mala- 

 costraca. The Mysida? stand much nearer to them than do 

 the Euphausiidte in the structure of the second pair of 

 antennaj (§§ 18 and 22), in the structure of the limbs, in the 

 development of the larva?, in the presence of the f ureal rami 

 in the earlier larval stages (§18), in the shape of the heart, 

 and in tlie presence of a conical projection for the orifice of 

 each vas deferens ; they appear to me to be the lowest of the 

 Eumalacostraca. 



27. The old division into Thoracostraca and Arthrostraca 

 strikes me as being quite untenable even when (with Grobben) 

 we have excluded the Stomatopoda as being a section of equal 

 value. The arrangement appears to me to be based alto- 

 gether too much upon only two conditions — the presence of a 

 shield and of stalked eyes, as opposed to absence of a shield 

 and sessile eyes, — and, moreover, none of these characters is 

 constant (Tanaidai, Cumacea). I consider that the Eumala- 

 costraca can be arranged much better in three *di visions, of 

 which the first will contain the Mysida, Cumacea, Isopoda, 

 and Amphipoda, while the second comprises the Euphau- 

 siida and Decapoda. The first division possesses a lacinia 

 mohilis upon the mandibles / eight segments in the limbs, of 

 ivhich the last segment is cheliform and the first several times 

 shorter than the second, while there are five segments before the 

 knee ; a marsupium ; larvce which are at first motionless and 

 have a peculiar development; an elongated heart; shorter or 

 longer processes jor the orifices of the vasa deferentia ; and no 

 spermatophores : while the second division is distinguished by 

 having mandibles without a lacinia mobilis ; limbs composed 

 of seven segments, of which the first is almost as well developed 

 as the second, while before the knee there are only four seg- 

 ments, of which the fourth is certainly homologous with the 



