156 PAXTOPODA. 



Plumularia), which are chosen by them as hosts. Dohrx assumes 

 that the larvae, after attaching themselves to the Hydroids by the 

 help of the fiagellae, throw off during a moult the two posterior 

 pairs of limbs that carry the latter, and pass through the oral 

 aperture of the polyp into its gastral cavity. They are certainly 

 found later in such a position, and here pass through the further 

 stages of their development. 



The tendril-like fiagellae seem not to occur in all Phoxichilidia, for R. aox 

 Lexdexfeld has described a larva of Ph. plumulariae not distinguished in any 

 way worth mentioning from the usual Pantopodan larva. This larva further 

 differs from other Phoxichilidia in its manner of life ; it does not penetrate into 

 the polyps, but only attaches itself to them by the help of its pincers and by 

 burying its beak in the host's body at the base of the head. The larva remains 

 in this position until it has almost attained the form of the adult animal. 

 We may gather from v. Lexdexfeld's description that the further development 

 of the forms discovered by him takes place as in other Phoxichilidia, for he also 

 mentions a two-limbed stage. 



It has already been stated that the larvae cast off the fiagellae and 

 limbs at ecdysis (Semper, Dohrx). The larva moults several times 

 (Fig. 73 B), the second and third pairs of limbs degenerating 

 completely (Semper); but, according to Adlerz, some vestiges of 

 the posterior pairs are retained (Fig. 73 C and D), and it is in 

 place of these that the second and third limbs of the adult arise. 

 The larvae, several of which often occur in one polyp, with their 

 large anterior limbs, have a very peculiar appearance (Fig. 73) in 

 this stage. In the following stages the limbs are found to degenerate 

 still further (this is also evident from the figure given by Adlerz), 

 but, with the bukdncrs of the intestines, the rudiments of the 

 posterior segments begin to appear. The ganglia of these develop 

 and the outgrowths of the body-wall which yield the limbs soon 

 appear (Seaiper, Adlerz). These processes seem, on the whole, of 

 the same nature as those before described. When three pairs of 

 ambulatory limbs have formed, and the fourth is present as a 

 rudiment, the young Phoxickilidium leaves the polyp and leads 

 a free life. 



4. General Considerations. 



Although much has been written as to the relationships of the 

 Pantopoda, these are still far from clear. The ontogeny of these 

 animals, as far as it is now known, unfortunately throws little light 

 upon the subject. In comparing the Pantopoda with other divisions 

 of the animal kingdom, attention is turned chiefly to the Crustacea 

 and the Arachnida. The form of the larva is of the greatest 



