THE PYCNOGONIDS. 25 



typical Nauplius to pass into the adult. During the growth of 

 the walking legs the second pair of appendages of the Pantopod- 

 larva has increased a little in size, but the third pair loses its 

 spines and the whole appendage becomes a simple prolongation 

 of the embryo. At a later stage, when the larva has increased 

 in size, this third pair grows out again to form the ovigerous legs. 

 In Pallene we have seen that the first, fifth and sixth pairs of 

 appendages appear simultaneously in the embryo. The seventh 

 comes in very much later, and the third after the seventh*. The 

 second did not appear at all in the ontogeny, so that in the 

 young Pallene the only appendages in the young embryo that 

 correspond to those of the Pantopod-larva are those of the first 

 pair. The development of Pallene has become so much abbre- 

 viated that there is only a trace of the true Pantopod-larva 

 found in its ontogeny. 



Phylogeny. 



There is a general agreement that the Pycnogonids are to be 

 placed within the large group of Arthropods, but after this there 

 is the greatest divergence of opinion as to which group of Arthro- 

 pods they are most nearly allied. In general there are two 

 prominent categories to which all or nearly all of these theories 

 may be referred. One lot of workers believed in a Crustacean 

 relationship, and another lot placed the Pycnogonids amongst 

 the Arachnids. It is needless to give here the reasons assigned 

 for these opinions, as Prof. Dohrn has given in his monograph 

 of the Pantopoda of the Gulf of Naples a most complete and 

 exhaustive bibliography of the literature. The two most import- 

 ant views which we have at present are those of Dohrn and of 

 Hoek, but, as the latter agrees with much that the former has 

 given, we may consider the two together. 



Prof. Dohrn's earlier view of the relationship of the Pantopod- 

 larva to the Nauplius he has completely given up in his more 

 recent papers. In an appendix to a paper in the Archives de 

 Zoologie experimental, Dr. Hoek gives a summary of Dohrn's 

 recent theory as to the phylogenetic position of the Pycnogonids, 

 and has at the same time contrasted his own views with Dohrn's, 

 so that a translation of a part of this review will best bring out 

 the resemblances and differences of their opinions. 



