462 Prof. K. Grobben on the Oenealogy and 



case, although I regard the fapt as worthy of notice, and I am 

 inclined to consider this agreement as only of secondary 

 importance. 



With regard, however, to the absence of the above- 

 mentioned typical Copepod characters in the case of the 

 Cypris-Yxko. larva of the Cirripedes, it appears to me that we 

 ought not to expect to find these characters at all in the larva 

 in question. A common origin for Copepods and Cirripedes 

 is not to be taken to mean that the Cirripedes sprang from 

 typical Copepods {i. e. of the Eucopepod type), but that they 

 arose from an ancestral form which was common to both groups, 

 and in which those most typical Copepod characters were not yet 

 developed. The ancestral form was consequently an animal 

 in which, to refer to what are riglitly indicated in this con- 

 nexion by Korschelt and Heider as Copepod characters, the 

 paired lateral eyes, as well as a broad dorsal shield, were still 

 present, and the conversion of the second maxillse into the 

 double pair of maxillipeds had not yet set in, while the thoracic 

 feet perhaps agreed in shape with those of Arguhis. 



On the same grounds is to be found the solution of the sup- 

 posed difficulty raised by Hoek *, that the CyprisAx^Q larva, 

 which is so characteristic of the ontogeny of the Cirripedes, 

 is altogether absent in the development of the Copepods. The 

 Cypris-\Q.x\2i of the Cirripedes is a typical Cirripede stage, and 

 was acquired by these Crustacea at a period when they had 

 already separated from the ancestral form which was common 

 to the Copepods as w^ell as to themselves. 



The Malacosteaca. 



The Malacostraca constitute a well-defined natural group. 

 In the Leptostraca {Nebalia) there are preserved for us 

 remnants of an old Crustacean type, which may with justice 

 be regarded as being very closely allied to the ancestral form 

 of the existing Malacostraca. On the other hand the 

 Leptostraca exhibit peculiarities which remind us of the 

 Euphyllopods. 



As primitive characters of Nebalia, when contrasted with 

 the other Malacostraca, we must regard the number of the 

 abdominal segments, which is one in excess of that found in 

 the remainder of the group, the preservation of the furca, the 

 foliaceous shape of the thoracic appendages, which represent 

 a mixture of the Schizopod and Phylloj)od foot, and lastly in 

 all probability also the shape of the shell. 



* P. P. C. Hoek, " Report, on tlie Cinipedia collected by H.M.S. 

 ' Challenger' during the years 1873-76 : Zoology, Part xxv.," 1883, p. 17. 



