378 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Vermes. 



Development of Worm Larvae.* — J. W. Fewkes has some rather 

 scattered observations on the development of certain worms. 



1. Prionospio tenuis. It is pointed out that defensive setae or 

 spines are only found on free-swimming annelid larvae, and this fact 

 leads to the suggestion that they are special organs for defence, rather 

 than " ancestral features," descended from fossil forms, which, according 

 to A. AgassiZj they sometimes closely resemble. 



2. Spio sp. This larva is telotrochal, and has a large preoral lobe 

 with an equatorial ring of cilia and embryonic spines, which arise 

 from ear-like backward projections of the head. Scattered pigment- 

 spots, but no cephalic eye- spots are present. When the larva is 

 alarmed the spines on its body are raised, and project at all angles 

 to their point of origin. 



3. Aricidea sp. There is a resemblance to Spio, but also certain 

 points of distinction ; the oldest larvae have the long provisional setae, 

 but not the other cephalic appendages of the larval Spio. 



4. A polytrochal larva, taken about the end of the summer, had two 

 flat circular ear- like appendages (" auricles ") on the sides of the head. 



5. Telepsavus (?). The larval forms doubtfully referred to this 

 genus are very common at Newport ; it is so large as to be easily 

 distinguished by the naked eye as it swims about in the water. 



6. Phyllochcetopterus sp. This larva closely resembles the pre- 

 ceding, but is distinguished by the absence of lateral cephalic tentacles. 



7. Nephthys sp. The youngest larvae have a great resemblance to 

 those of Polygordius, but the pattern of colour on the anal pole is 

 characteristic. A movement of the eye-spots from the head to the 

 fourth body-segment was noticed, but the means by which it was ac- 

 complished were not quite clear. 



8. Lepidonotus squamatus (?). The youngest larvae were mono- 

 trochal. 



9. Nereis sp. The mandibles were seen to be well developed at an 

 early stage. 



10. Pilidium recurvatum. This name is provisionally given to an 

 interesting form, which has many structural relationships to Tornaria 

 {Balanoglossus') and Actinotrocha (Phoronis). The interior of the 

 larva is occupied by an CBSophagus, and " an amniotic cavity, which 

 contains a growing Nemertine worm " ; the oesophagus is continued 

 into the intestinal cavity of the young Nemertine. This form passes 

 through a remarkable metamorphosis in which, however, no part of 

 the nurse is unabsorbed, even the pigmented regions of the amnion 

 being detected in an enlargement at the hinder end of the worm. 

 The author regards this absorption of the larval envelope as one more 

 characteristic pointing to the close affinities of the Nemerteans with 

 the Echinodermata. 



11. Polygordius. The Lovenian larv£e are among the commonest 

 of those found at Newport ; in the figures here given attention is 



* Bull. Mus. Comp. Zool. Oamb., xi. (1883) pp. 167-208 (8 pis.). 



