219 



sites, one on each side of the anterior division of the body, both turning their 

 heads towards that of their host (see fig. 1). On examining the specimens more 

 closely, they were found to be of rather different size and different degrees of 

 development, though evidently representing the very same species. The smallest 

 specimens (fig. 1 a) had all the characters of a normal Bopyrid-larva in the 1st 

 stage, and exhibited a strong resemblance to the well-known larva of Phryxus 

 abdominalis (cf. PL 91 below), the number of legs being only 6 pairs, and 

 the antennse, pleopoda and uropoda being tipped with slender bristles. In some- 

 what larger specimens (fig. 16) the antennse had lost their bristles, and assumed 

 the appearance characteristic of the Mieronisci, looking merely like simple inarti- 

 culate processes. The 6 pairs of legs exhibited likewise a much more clumsy 

 appearance, showing scarcely any trace of articulation, though terminating in a 

 sharp hook-like point, and behind them a 7th pair of legs was seen in process 

 of formation as 2 comparatively small rounded tuberosities. The pleopoda were 

 still tipped with bristles, but of very small size, whereas the uropoda were wholly 

 devoid of such bristles, and their rami were only present in the form of slight lobes. 

 In other specimens (fig. 1 c.) of larger size and with the body more produced, the 

 7th pair of legs had lengthened considerably so as to project laterally, though 

 showing as yet no trace of a terminal claw (see fig. 1 c., p 7). In this 

 stage, which otherwise did not difier much from the preceding one, the 

 Microniscus agrees rather closely with one of the 2 specimens recently figured 

 by Dr. Hansen in his work on the Isopoda, Cumacea and Stomatopoda of the 

 German Plankton-Expedition. Finally, in the largest specimens (fig. 1 d), which 

 exhibited all the characters of a normal Microniscus calani, all the 7 pairs of 

 legs were distinctly developed and of exactly the same structure, representing 

 indistinctly articulated grasping organs, (fig. 1 d. p.), and the uropoda had leng- 

 thened considerably, the outer ramus projecting far beyond the inner, and exhibiting 

 a -few small hairs at its tip (see fig. 1 d. urp.). In all the specimens, distinct 

 though rather small eyes were present on each side of the flat, semicircular 

 cephalon, and the lateral parts of the segments were more or less acutely pro- 

 duced, giving the sides of the body a jagged appearance. 



Another form of Microniscus was found in a different locality, clinging 

 to a deep-water Calanoid, Mdridia longa Lubbock (fig. 2). This form (fig. 2 a), 

 of which 2 specimens were secured, agreed in all essential characters with that 

 found on Pscudocalanus doiujatu*, but was of somewhat larger size, and had the 

 lateral parts of the segments less produced. It differed, moreover, in the total 

 absence of visual organs, as also in the structure of the uropoda. \YluTeas in 

 the other form, the inner ramus of these appendages exhibited a very rudimen- 



