196 On the Development of the Pycnogons. 



The larvae of Pycnogonuin, Achelia and Zetes, resemble 

 the species just described in their general contour, although, 

 as might be expected, there are certain characteristic dif- 

 ferences. They all possess foot-jaws similar to those described, 

 from which are produced the filamentary appendages as in 

 Nymphon. These organs in all the species examined are kept 

 constantly in motion — a sort of " whipping action," which it 

 seems probable may assist in impelling the little animal through 

 the water. The presence of foot-jaws in the larvae of these genera 

 is a very singular circumstance, for the mature animals are 

 quite destitute of them. Excepting, therefore, for the fact of 

 having obtained the mature animal with the larvae attached, 

 one might reasonably be disposed to question the possibility 

 of the immature animal being in apparent advance of its 

 parent in certain respects, for foot-jaws are undoubtedly a 

 type of elevation. 



Much has yet to be learnt respecting the development of 

 these animals, and so far as one can judge from analogy, all 

 must undergo some singular metamorphosis between the two 

 stages known, the earliest and the mature. Those observers 

 who have opportunities of obtaining living specimens would 

 do well to endeavour to make out the development of Pycno- 

 gonum littorale, as it seems highly probable it will prove quite 

 distinct from those just described. Hitherto it has eluded the 

 writer, possibly some one else might be more fortunate. 



EXPLANATION OP THE PIGTTEES. 



Fig. 1. Larva of Nym.phon, as attached to parent (mag- 

 nified). 2. Second stage of the same animal, ditto. 3. 

 Third stage of the same, ditto. 4. Larva of Phoxichilidium 

 coccineum as attached to parent (magnified). 5. Embryo of 

 Pycnogonum littorale, ditto. 6. Larva of Pycnogonum littorale, 

 ditto. (All represent the under surface, to show origin of 

 rudimentary limbs.) 



