24 Prof. M'lntosh's Notes from the 



marked by complex folds. Dorsally and externally is the 

 median mesentery, whilst inferiorly is the ventral mesentery 

 enclosing the blood-vessel, and at intervals the plexus of 

 muscular fibres from the oblique muscles and the gut itself, 

 making the arch over the ventral vessel. 



Thoracic Glands. — The thoracic glands, or anterior seg- 

 mental organs of some, have been the subject of various 

 interpretations. Thus Ehrenberg * in Amphicora sabella 

 and Grube in Spirographs spallanzani thought them re- 

 productive organs. Oscar Schmidt f more or less followed 

 this interpretation, though he associated them also with an 

 excretory function. He describes them as two short sacs 

 opposite the first bristle-bundle in Amphicora mediterranea, 

 each with a duct leading obliquely forward to join its fellow 

 and to open in the mid-dorsal line behind the branchise. 

 Williams, again, did not allude to these organs, but located 

 the segmental organs of Sabellids and Serpulids in every 

 abdominal segment, each with an external and an internal 

 opening. Ley dig and Huxley (the latter in Filograna) 

 added little more than a notice of them. De Quatrefages 

 considered them in the Serpulids as blind hepatic sacs con- 

 nected with the stomach. Claparede (1870) thought them 

 modified segmental organs which in the Serpulids secreted 

 mucus, the ordinary segmental organs occurring in all the 

 abdominal segments of such as Psygmobranchus. Cosmovici 

 interpreted them as excretory organs or " Organs of Bo- 

 janus" ; whilst the segmental organs in the posterior region 

 transmitted the ova and sperms. Langerhans termed them 

 head-glands in Sabella (Potami/la) stichophthalmus aud Eu- 

 chone i*osea, and that they opened dorsally. A. G. Bourne J 

 (1883) considered these organs in Haplobranchus tubiparous 

 glands or modified nephridia, and he mentions no ducts. 



In his account of the segmental organs of Branchiomma 

 Brunotte § describes, after Claparede, the thoracic glands as 

 thoracic segmental organs, and situated in the first and 

 second segments, thus being less developed than in Spiro- 

 graphis spallanzani, and even than in Chatozone and Myxicola, 

 the former species having them in all the thoracic segments, 

 the latter in more than two segments. The author interprets 

 their structure as glands formed by the volutions of two 

 tubes, and in his figures (pi. i. tig. 31, and pi. ii. fig. 40) 

 shows the ccelom as filled by the coils of these, yet in pi. ii. 



* Mitth. Verh. Ges. Nat. Freunde, Berlin, 183G. 



+ Neue Beitrage Nat urges, der Wiirmer-Reise nach Faror, 1848, Jena. 



\ Quart. Journ. Micros. Soc. vol. xxiii. p. 168. 



§ Recherches Anat. Branchiomma, p. 59 (1888). 



