a Parasite o/'Cjdippe densa. 33 



No doubt it will have seemed strange to the readers of the 

 title of this Note that deep-sea Annelida, with eyes so well 

 developed and with natatory organs, should pass through a 

 stage as parasites, which might have been more readily ad- 

 mitted in the case of Annelida shapeless, blind, and degraded; 

 and yet it seems to us very evident that the larvaj we have 

 described, and perhaps those of other Alciopids also, present 

 this condition of temporary endoparasitism for this very end, 

 that the eyes and feet, under such circumstances, may have 

 time and the conditions favourable to their development and 

 growth. 



In conclusion, it may be demanded to what form of the 

 Alciopids these larvas are to be referred. In the most advanced 

 stage to which we have traced them, they cannot be assigned 

 to any known genus : but whether the tentacles of the oral 

 segment continue short or are lengthened in the progress of 

 development, we shall have a new genus, characterized prin- 

 cipally by the four antennaj, the two tentacles of the oral seg- 

 ment, and by the difference of structure of the first three pairs 

 of feet from the rest, as well as by other characters of generic 

 value, which may be gathered from the description we have 

 given. The subjects being larv», and not adult animals, we 

 cannot at present give a complete and positive character ; 

 nevertheless, being convinced that the genus is new, we pro- 

 pose to distinguish our Annelid by the name oi Alcio2yina pa- 

 rasitica. 



Subsequently to these studies of ours, Herr Buchholtz, of tlie 

 University of Greifswald, having observed, at Naples also, in 

 the month of May, similar larvae in the same Cydippe^ on 

 collating these with ours, has found that they are of the same 

 genus, but differ as to the number of the large setee, which are 

 four instead of two, and not muricated, accompanied by a 

 dart. These observations, while they confirm our suspicion 

 that there are other kinds of Alciopids which resemble that 

 described by us in the mode of life at first, present a new 

 incitement to further investigations of the subject. 



EXPLANATION OF PLATE V. 



Fig. 1. Cydippe densa, Forskal, with parasitic larvae inside. The stomach 



and principal {j^astrovascular canals injected. 

 Figs. 2, S, 4. Ciliated larvae, first stag'e. Natural length 1 millim. 

 Fig. 5. Larvae, second stage ; the cilia gone. 

 Figs. 6, 7. Larvae, third stage, in which the antennae begin to appear and 



the feet acquire greater development. Nat. length 2-3 millims. 

 Fig. 8. Larva, fourth stage, with the development of the antennae, eyes, 



and feet more advanced. Nat. length 4 millims. 



Ann. & Mag. N. Hist. Ser. 4. Vol.iv. 3 



