2 6 PYCNOGONIDA. 



going, also a couple of larvse on the second stage, but not of the same degree of development. In 

 the younger of these larvae, pi. II, fig. n, the three foremost pairs of ambulatory legs are all developed, 

 and, contrary to what commonly is the case, all developed to the same degree. The byssus-gland is 

 also earlier developed than usual. In the somewhat older larva, fig. 12, the first pair of ambulatory 

 legs are, as usual, much more developed than the second pair, and the third pair is not even 

 to be seen. 



Of Nymphon Sluiteri I have also drawn a phase of the second stage, pi. II, fig. 17, viewed from 

 the side, and fig. 18, viewed from below, but they show nothing remarkable with regard to the develop- 

 ment of the limbs. 



Of Pycnogonum littorale I have an interesting drawing, pi. I, fig. 4. The specimen was taken 

 a score of years ago by the present doctores, Mr. Hector Jungersen and Mr. Johannes 

 Petersen, at Frederikshavn without particular statements as to the circumstances in which it was 

 found. It can be no other than a larva in the close of the second stage of a Pycnogonum s. str. , but 

 from Frederikshavn and upon the whole from Denmark we know of no other Pycnogonum than P. 

 littorale, which moreover is commonly found on the locality in question. The embryonal limbs have 

 already quite disappeared, and no traces are to be seen, either from the upper side, represented here, 

 or from the lower side. That these limbs have disappeared is no wonder, as they usually do so, if 

 not so quickly, at all events in a short time; more remarkable is the absence of the chelifori. In 

 other instances the chelifori are embryonal limbs which are kept throughout the life of the animal, if 

 not always with a fully developed chela, at all events, though, with fragments of it, and only in a 

 few forms, the genera Pycnogonum and Phoxichilus , the so-called order <,.Acerata of Sars, and in 

 his family Colosscndcida, the chelifori are quite wanting in the full-grown animal; there is, however, 

 a great possibility that the chelifori of the last-mentioned family are not thrown off until an advanced 

 stage, after the close of the larval development. Such, at all events, is the case in Colosscndeis 

 angusta (and gracilis] according to the observations of Hoek, which observations I shall here aug- 

 ment very much (in another Coloss. (macerrima) I have found the chelifori thrown off already in a 

 very young animal). The larva of Pycnogonum drawn here, is, judging by the development of the 

 ambulatory legs, in the close of the second stage, all three pairs of legs having reached the full seg- 

 mentation, also the claw. The body and the legs are smooth and naked, without the thick, rugged 

 exoskeleton distinguishing the grown Pycnogonum, and only the oculiferous tubercle and the three 

 knobs in the middle line of the back remind of the rugged appearance of the animal. The first seg- 

 ment of the trunk is uncommonly and unproportionally large. 



The genera Pallene and Pseudopallene are distinguished from the other Pycnogonida, not only 

 by the above mentioned absence, or rudimentary state of the embryonal legs, but also by the two 

 foremost pairs of ambulatory legs arising contemporaneously, growing, and attaining to a considerable 

 development, before the growth of the third pair of legs begins. Of Pallene I have examined two 

 species, Pall, brcvirostris and Pall, hastata. The former, Pall, brevirostris, is given on a rather early 

 stage, in which the two pairs of ambulatory legs are somewhat short and thick, with a single con- 

 striction in the middle besides the claw, pi. I, fig. 16; a special distinction is the separation, already 

 mentioned in the foregoing, of the byssus-gland in particular dermal glands, each with a byssus-thread 



