Respiration in Invertebrate Animals. S97 



indicates a transition from the typical Amphitrite to the genns 

 Terebella (fig. 1. PI. XIV.). In all the species of the latter genus 

 the branchial organs appear under the form of blood-red tufts 

 (fig. 1, a), proceeding from three or more separate root-vessels on 

 either side of the occiput. The vessels divide for the most part 

 dichotomously, forming an arborescent bunch of naked florid 

 branches : each ramuscule is enclosed in a delicate cuticular en- 

 velope (fig. 3, «^) perfectly destitute of cilia, and conveys to its 

 extreme end a single vessel looping upon itself (tig. 3,?/?). 

 Although extremely transparent and attenuated, the epidermal 

 coating must include contractile fibres, since each branch may be 

 emptied, rendered bloodless and shrivelled, by the compression of 

 the parietes. This provision for reinforcing the central circu- 

 lating powers exists in various parts of the blood-system of the 

 Annelida. It may be affirmed, generally, that in all true Tere- 

 bella the branchiiB occur under the character of naked, unciliated 

 blood-vessels restricted to the occipital rings of the body. In 

 T. nebulosa (fig. 1, A) they constitute thick, florid, resplendent 

 tufts ; in T. cunchilegia they are fewer in number and less pro- 

 minent. In the smaller species * the cephalic tentacles (fig. 2) 

 of the Terebellce constitute, unquestionably, auxiliary organs of 

 respiration ; they are copiously penetrated by the chylaqueous 

 fluid ; they carry vibratiie cilia on their inferior side (fig. 2, g) ; 

 they are capable of injection by the chylaqueous fluid ; they open 

 directly into the peritoneal chamber ; they are tubular, flattened 

 filaments, furnished with strong muscular pai"ietes; they are 

 admirably fitted to aerate the chylaqueous fluid ; they are inces- 

 sant in their motions ; touch is obviously one of their functions ; 

 they also act as prehensile organs, conveying food to the mouth ; 

 but they are also organs of locomotion ; they are fixed suctorially 

 on a surface in advance of the animal, and used as ropes for 

 hauling forwards the body. 



In Terebella conchilegia, tubicolous and sedentary in its habits, 

 the cephalic tentacles are inferior to those of T. nebulosa in num- 

 ber and size. They are differently configurated ; they approach 

 the prismatic in outline ; in transverse section they present a tri- 

 radiate shape ; in minute structure and mechanism of action, they 

 differ slightly from those of the latter ; they are not for loco- 

 motive purposes ; hence their reduced size and diminished 

 number. 



It is not a little curious that in the Terebellce these organs, 

 which are homologous with true cirri, should be so richly pro- 

 vided with vibratiie cilia, while the true-blood branchise are en- 



* Several undescribed small species will in a future number of the 

 'Annals' be fiariu'ed and defined. 



