570 RECORD OF CURRENT RESEARCHES RELATING TO 



this arrangement is found in the Euphrosynida, Amphinomida, Aphro- 

 ditida, Polynoida, Phyllodocida, Syllida, Nereida, Eunicida, Chlor- 

 haeminida, and Amphictenida. 



(2) Tlae nerve trunks are placed externally to the muscular layer 

 and in the hypodermis ; the oblique muscles taking their origin from 

 a transverse band set superiorly or laterally to them, as in the Siga- 

 lionida, Hesionida, Ariciida, Ch8etoj)terida, Spionida, Cirratulida, Am- 

 pharetida and Terebellida. 



(3) The trunks are embraced by the closely approximated ventral 

 or other longitudinal muscles ; as in the Glycerida and Telethusida. 



(4) In the substance of the ventral longitudinal muscles, as in the 

 Hermellida, 



(5) Beneath the ventral long muscle, or at its margins, or inter- 

 nally to the circular layer, as in some Sabellida and Serpulida. 



In some families there are neural canals, which are largest in the 

 Spionida, and are best seen in Magelona. 



Gills of Serpula.* — Dr. L. Lowe, of Berlin, deals with the struc- 

 ture of these organs, and enters into the question of the relations of the 

 Annelides to the Vertebrata ; his observations are based on the form 

 known as Spirorbis, which differs from Spirographis, already examined 

 by Kolliker and Claparede, in the absence of the cartilaginous gill- 

 skeleton. 



About thirty branchial filaments spring from a branchial lobe 

 on either side of the mouth ; each of these has the form of an 

 elongated cone, in which it is possible to distinguish a shaft and a 

 vane ; the former, which decreases in size towards its apex, consists 

 of (1) an external cuticle, (2) a closely applied cellular layer, (3) a 

 vascular layer, and (4) a cuticle ; the vane is made up of a central 

 part, which is the continuation of a vascular layer, and of a marginal 

 portion, which consists of a cuticle and a chitinogeuous epithelium ; 

 all these structures are described from a histological standpoint, and 

 the changes which the gill undergoes during growth pointed out ; the 

 concluding portion of the paper is occupied by an extremely ingenious 

 comparison of the gill-apparatus of these forms with the branchial 

 clefts of the Vertebrata. 



Two observers, working independently, have lately shown that 

 the Eustachian tube and the tympanic cavity are primarily formed 

 by a diverticulum of the oral cavity, while the external auditory 

 meatus is formed by such part of the first gill-cleft as is not 

 obliterated ; Dr. Lowe has confirmed the essential points of these 

 observations, and gives a figure of an embryo of the sheep in 

 support of them ; this displays the following points ; from the oral 

 cavity there is given off outwards and backwards a long narrow cleft, 

 which is the rudiment of the Eustachian tube ; this at its outer end 

 widens out and forms the tympanic cavity ; there comes to meet this 

 an invagination of the epidermis which forms the external meatus, 

 while between these two processes there is a region in which appear 

 the auditory ossicles and the tympanic membrane. Turning now to 



* 'Zeitschr. wiss. Zool.,' xxxii. (1876) p. 158. 



