THE PELAGIC WORM TOMOPTERIS. 9 



very large size and then appear as very characteristic ova. Finally 

 these break loose and pass into the body-cavity. It is probable 

 that they normally pass thence to the water by rupture of the body 

 wall of the parent, but whether fertilization takes place prior to this 

 is uncertain. Curiously I ha've not lately met with the male form. 

 Carpenter describes it as having a long tail-like prolongation bearing 

 four or five minute appendages wherein are developed spermatozoa. 

 The tail-like prolongation is indeed given as being present in both 

 sexes of different species but so far in the present species I have 

 not seen any trace of it in the females. Of males, I have not been 

 able to examine any. 



The embryology is little known and we only become familiar 

 with the animal in an advanced larval stage. The earliest one 

 known to Dr. Carpenter belonged to a species having no posterior 

 antennas in the adult state, but in the larval it had no anterior 

 developed while the posterior were very obvious and bore each a 

 distinct bristle, and were of comparative large size. The tentacular 

 cirri (t c.) were short, and approached the form of the succeeding 

 partially developed parapodia, saving that they (the tent cirri) pos- 

 sessed stout setae like the posterior antennae. It is very interesting 

 to note that the species figured here (Fig. 10), shows in each 

 posterior antenna a distinct claw-like bristle, and this inclines me 

 to the belief that these organs are not antennas but are vestigial 

 tentacular cirri. The large tentacular cirri in the larval stage ap- 

 proach very closely in form to the parapodia and differ principally in 

 the presence of setae. The secondary antennas again approach closely 

 in larval life to the appearance of the tentacular cirri, so the inference 

 is clear. It is only with the attainment of maturity, that this organ 

 becomes reduced and difficult to homologize, and even then, as seen 

 in our figure, there can in some species be traced distinct setae. 

 In the larger T. onisciformis (Carpenter) this appendage however 

 entirely disappears in adult life. 



Rosette-shaped organs have been made out at the bases of 

 certain feet ; their function remains still obscure. 



EXPLANATION OF FIGS. 10 TO 15, PLATE 1. 



Fig. 10. Entire adult Tomopteris (female) ; a. anterior antenna ; 



a 1 , posterior antenna (vestigial tentacular cirrus) ; t c. 



tentacular cirrus ; p. a parapodium. X 17. 



Fig. 11. Parapodium, nt. notopodium ; nr. neuropodium ; ov. ovary. 

 Fig. 12. Ovum. no. nucleolus or germinal spot ; n. nucleus or 



germinal vesicle ; v. vitellus ; v m. vitelline membrane, 



X 200. 



