ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 731 



an extent four times as great. The first new genus SccBorJiynchus 

 (1 sp.) has an extent of more than 19 cm., a gigantic size as compared 

 with the dimensions of its nearest allies. The most abundant species 

 of Ni/mphon is the largest of that extensive genus ; and one of the two 

 new species of the other new genus Pallenopsis is more than twice as 

 large as any of the species of allied genera (JPallene, PJioxicJiilidium, 

 Anoplodactylus), which are known only from the littoral zone or 

 comparatively shallow water. 



It is, further, interesting to note that in a number of forms the 

 visual organs (ocelli) are rudimentary and destitute of pigment 

 (Colossendeis colossea, C macemma, Scceorhynchus) or entirely absent 

 (Colossendeis angusta). On the other hand, in Pallenopsis the ocelli 

 are relatively of unusually great size. All the other species are 

 known to occur also in shallower water, and the ocelli are of the 

 ordinary form. 



SccBorhynchus and Colossendeis are of especial interest as showing 

 clearly from anatomical evidence the complete independence of the 

 accessory legs and first pair of ambulatory legs, which has been 

 already proved by Dohrn from embryological data. The accessory 

 legs have been something of a stumbling-block to those who would 

 trace the Arachnid affinities of the Pycnogonida by a direct homology 

 of their appendages, and in the view of the author it is impossible to 

 homologize the Pycnogonid appendages with those of the Arachnida 

 unless a segment of the latter has been suppressed somewhere between 

 the chelicer^ and ambulatory legs. The possibility of such a sup- 

 pression is shown by the fact that in a number of Pycnogonida the 

 process has taken place, and without leaving a trace in the embryo- 

 logical record. Thus in Pallene the palpi are wholly wanting, both 

 in the adult and in the larva. Granting that such a suppression may 

 have taken place, the homology of the Pycnogonid and Arachnid 

 appendages is manifest. This suggestion must, however, be taken for 

 what it is worth, for it is easily possible that the external resemblances 

 of a Pycnogonid to an Arachnid are those of analogy only, and have 

 no morphological significance. This is the more probable from the 

 extreme variability of the three anterior pairs of appendages in 

 position and structure. 



One more point of interest may be noted. In Scceorhynchus the 

 anterior pair of appendages Ccheliceree or " antenna ") present very 

 decided sexual differences. This has not before been observed in the 

 Pycnogonida, and furnishes another illustration of the surprising 

 modifications which the anterior pairs of appendages undergo in this 

 group. 



Hydrachnida of the Lake of Geneva.* — F. Konike here gives a 

 revision of the nineteen Hydrachnida described by Lebert. The 

 author cannot agree with Lebert in regarding the epimera as foot- 

 joints, but takes the view of Claparede, who did not consider them 

 to be part of the feet. So, again, the palpi are not six- but five- 

 jointed, for the basal joint of Lebert is regarded as a part of the 



* Zeitschr. f. wiss. Zool., xxxv. (1881) pp. 615-29 (1 fig.). 



