INVEKTEBRATA, CRYPTOGAMIA, MICKOSCOPY, ETC. 



437 



(3) The structure of the Sheath of the Proboscis and of the con- 

 nected parts. — In E. Proteus the sheath is about 2 mm. long, and the 

 diameter about O'i mm. It consists of two eylindiiform rolls of 

 muscular substance, one internal and the other external ; the former, 

 or true sheath, is closed posteriorly, save only to give passage to the 

 fibres of the retractor prohoscidis ; the latter is open at both ends. 

 Fibres of connective tissue pass into these two muscle plates, horizon- 

 tally into the exterior, and obliquely into the interior one ; this gives 

 rise to a difference in the appearance of transverse sections. The 

 retractor proboscidis is attached to the base of the inner cylinder, and 

 takes an upward direction. Not far from the lower end of the re- 

 ceptaculum jiroboscidis there is a ganglion which is oval in form ; 

 this is best seen, however, in E. angustatus, where it is distinctly 

 composed of an outer and of an inner layer of cells, which are so 

 packed together as to be pentagonal or hexagonal in form. There 

 is no envelope to the ganglion. The separate cells give off fibres, 

 several of which always unite to form nerves, and of these six well- 

 developed rami can always bo easily detected. The course of the 

 anterior and posterior median nerves and of the two antero-lateral 

 and postero-lateral is then shortly traced. 



(4) llic Female Generative Organs. — These have excited the interest 

 of a number of observers, and they are, without doubt, worthy of 

 study. In E. Proteus, where it is somewhat longer than in E. angus- 

 tatus, the uterus is said to be comi)osed of fifteen cells, which are 

 thus distributed : two form the " bell," and two the muscular ring ; 

 behind the bell there are two elongated cells, at the base of which 

 there arc placed the two which are set opposite to the posterior orifice 

 of the bell ; these support the two lateral cells ; the mesbwork is 

 formed of another two, two invest the ligament, and an unpaired cell 

 is placed in front of the meshwork ; these last three appear to be 

 glandular in function. The way in which the ova pass into the boll 

 and the complicated structure of the vagina are then described. 



New Observations on the Nemertinea.* — Dr. Hubreclit gives a 

 brief account of the results of his work at Naples. In very many 

 Nemertincs there appears to be a third nerve-cord, in addition to tho 

 two lateral, and this occupies the dorsal median lino ; contrary to tho 

 results of most observers, the author states that, in some forms, he 

 has found the two lateral cords uniting at their posterior extremity, 

 and he states that the commissure of union lies supcriorhj to tho 

 intestine. A true " vagus " nerve ai)pcars to be present, while the 

 proboscis has a special system of nerve brandies, w'hich, arising from 

 the neiglibourhood of the anterior cerebral commissures, arc evidently 

 connected with tlio cerebral ganglion. Dr. Ilubrecht has found new 

 evidence to support his hypothesis of the respiratory activity of the 

 nervous tissue of these worms ; tho whole of this nervous tissue 

 appears to be impregnated with hiomoglobin, which is brought into 

 immediate contact with tlie sea-water by means of highly ciliated 

 and coiled canals. 



The metamerically arranged internal dissepiments noted by 



* 'Zool. Anzcig.,' ii. (187t)) p. 474. 



