IMMATURE SPECIMENS OF PENELLA FILOSA. 305 



the larva of Penella at the time when it attaches to the host has 

 a form not unlike this " mating-stage " of the Lerntca. That is, 

 it will closely resemble the youngest stage of the Penella vanans 

 series with the exception that the posterior or genital segment of 

 the thorax will not be as disproportionately long in comparison 

 to the rest of the body. Very probably this segment will not be 

 sharply distinguished from the abdomen, as in the case in Lerncea 

 of this age. A number of years ago Wierzejski ('77) described 

 certain larval Copepods from the gills of Loligo, Sepia and E/c- 

 donc at Triest and suggested that they might be the mating-stage 

 and younger larva of Penella various. His opinion was based 

 on the characters exhibited by the appendages. As figured, 

 however, these structures do not appear to be at all conclusive 

 with regard to this hypothesis and in general form the larvae 

 certainly do not at all correspond to what would be inferred 

 for the mating-stage of any Penella. Two minute immature 

 Copepods have been recorded which seem to fill the require- 

 ments better. These were described under the names Bacillus 

 elougatns (Lubbock, '60) and Hessclla cylindrica (Brady, '83). 

 The former was collected in the Gulf of Guinea, the latter off 

 Zamboanga in the Sulu Archipelago. Although not wholly 

 alike in all structural details, they agree in possession of a fili- 

 form shape, cylindrical cephalothorax with projecting second an- 

 tennse, short segmented thorax, with four pairs of limbs, and an 

 elongate hind-body devoid of lateral appendages and evidently 

 representing a fusion of the posterior part of the thorax with the 

 abdomen. Liitken in 1892 strongly urged that Bacillus elon- 

 gatus be regarded as a larva of Penella. He points out that 

 Bacillus elougatns is a pelagic form, in harmony with the fact 

 that the senus Penella infests " fishes or whales with a more 



o 



or less marked pelagic habit (Xipliias, Coryphcena, Exoccetus, 

 Diodon, Mola, Ptcropliryne, Hypcroodon, Bal&noptcra)" The 

 filiform shape of these larvae unquestionably suggests Penella and 

 the argument from habitat is significant. But, nevertheless, it 

 must be admitted that on a basis of present knowledge of the 

 forms a definite determination is not possible. We can only say 

 that Bacillus or Hessclla are almost certainly the young of ler- 

 naenoid copepods, possibly of Penellas. However this may be, 



