THE PYCNOGONIDS. 33 



question must remain an open one. It seems not improbable, 

 however, that the openings may be secondary and connected in 

 some way with the secondary presence of reproductive organs 

 in the appendages. 



I hope to have shown that these three objections are of 

 negative value, at any rate so long as the present uncertainty 

 surrounds them, and that we have sufficient grounds for a com- 

 parison in the early stages of development and in some of the 

 important adult structures of the two groups. 



The Pantopod-Larva. 



There is a general resemblance between the Nauplius of the 

 Crustacea and the larva of the Pycnogonids, but the differences 

 become greater and greater the more closely we examine the 

 two forms. In each the body contains three pairs of append- 

 ages, but those in the Nauplius show biramous structures, while 

 none of the Pantopod-larval appendages show such structures. 

 Moreover, the first pair of appendages of the Pantopod-larva is 

 chelate and innervated from the brain. Other characteristics of 

 the larva are the well-marked proboscis with its triangular oeso- 

 phagus, the mid-gut sending out prolongations into some of the 

 appendages, and the absence of any anal opening. 



Have we then any basis for the assumption that this Pantopod- 

 larva is a modified Trochophore of the Annelid ancestors % The 

 problem is very similar to that of a supposed relationship between 

 the Nauplius and the Trochophore, and in both cases an answer 

 exceedingly difficult to give. Prof. Dohrn believes that the 

 Pantopod-larva is to be regarded as a Trochophore with the 

 Pycnogonid characteristics reflected back upon it. Prof. Lang 

 believes in a similar process for the Nauplius. Without discus- 

 sing the latter, let us confine our attention to the possibilities of 

 the Pantopod-larva. 



What characters have been "reflected" on Dohrn's theory, and 

 what remains after these are removed ? Prof. Dohrn has given 

 us the answer. "... The absence of an anal opening, the pincers 

 of the first pair of appendages, the long claws with the accessory 

 spine, the structure of the proboscis with its triturating appa- 

 ratus and its ganglia, the form of the tegumentary glands and 

 their characteristic hairs, can only be considered as having been 



