462 Prof. K. Grobben on the Genealogy and 



case, although I regard the fact 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 

 Ci/prin-Vikc larva of the Cirripcdes, it ajipears to me that we 

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

 in question. A common origin for Co|>epods and Cirri pedes 

 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 wiiich those most typical Copepod characters were not yet 

 developed. The ancestral form was consequently an animal 

 in which, to refer to what are rightly 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 maxillre into the 

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

 feet perhaps agreed in shape with those of Argulus. 



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

 posed difficulty raised by Hoek *, that the Cyprifi-Mke. larva, 

 which is so characteristic of the ontogeny of the Cirripedes, 

 is altogether absent in the development of the Copepods. Tlie 

 CyprisA'AWS, 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 well as to themselves. 



The Malacostraca. 



The Malacostrr.ca constitute a well-defined natural group. 

 In the Leptostraca [Nehalia) 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 Nebalta, 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 

 foliaccous shape of the ti)oracic appendages, which represent 

 a mixture of the Schizopod and Phyllopod foot, and lastly in 

 all probability also the shape of the shell. 



* P. P. C. Hoek, " Report on the Cirripedia collected by H.M.S. 

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



