144 HOMOLOGIES. 



This animal, therefore, leans to the Planarian rather than the Nemertean type ; and on the 

 whole it would appear that, while the affinities of these groups are sometimes in accordance, 

 there can be little doubt as to the higher position of the latter in almost every respect. 



Balanoglossus. 



Two species of Balanoglossus dredged in the last cruise of the "Porcupine" (1870), in the 

 one instance by Mr. Jeffreys outside the Strait of Gibraltar, to the south of Tangier, in 128 

 fathoms, 1 and in the other by Dr. Carpenter off the Algerine coast, at a point intermediate 

 between Capes Falcon and Tenes, in 51 fathoms, 2 gave me an opportunity of investigating an 

 apparently intermediate type of much interest. Unfortunately, none of the specimens were in 

 good condition, either from rapid decay before being placed in spirit, or some other cause. None 

 of the fragments exceeded If inch in length, and the diameter at the collar or widest portion was 

 about f-ths of an inch. 



The general appearance of those dredged by Dr. Carpenter resembles the penis, the short 

 conical anterior end or " proboscis," with the overlapping collar behind, closely imitating the 

 glans penis, with its prepuce retracted. On the dorsum the "proboscis" is marked by a furrow 

 at its base, and, continuous with this on the body, two well-marked ridges course along the 

 median line. On the ventral aspect is a deep median furrow, a groove also being present on the 

 head in the same line. The body is rounded anteriorly, flattened posteriorly. 



The " proboscis " exhibits various appearances, from the bluntly conical form in contraction 

 to a more elongated and pointed contour in partial extension ; and it is evidently a very mobile 

 muscular organ. On reaching the collar, its base becomes contracted all round, so as to be 

 connected with the trunk only by a narrow pedicle, which is attached just over the anterior 

 opening or mouth, the whole having the appearance of an operculum or plug. The anterior end 

 or " proboscis " has lost its dermal layers in all the preparations, showing externally a tough, 

 translucent and slightly granular membrane, probably the representative of the basement- 

 membrane of the cuticular tissues. A considerable belt of circular muscular fibres forms the 

 next investment. In transverse section a large number of vertical lamellae are observed to be 

 arranged within the latter coat, in a divergent manner with regard to the central space. These 

 can readily be split from each other in a longitudinal direction, yet so intimately do the fibres 

 mix that in longitudinal sections their main direction is longitudinal, while they follow a trans- 

 verse direction in transverse section. Prom the shape of the region the lamellae become narrowed 

 in front and widened posteriorly. The nature of the specimens did not warrant a decision as to 

 the presence or absence of a terminal pore, but, from an examination of specimens in the living 

 condition, other authors, such as Delle Chiaje, 3 Keferstein, 4 Kowalewsky, 5 and Willemoes-Suhm, 6 

 have observed one. The posterior end of the "proboscis" in contraction fits into a kind of cup 



1 No. 36, surf, temp., 75° ; bottom, 55° Fahr. 



3 No. 50, „ 75°; „ 54° 7'. 



8 c Memorie sulla storia e not. degli/ &c, vol. iv, p. 117. 



4 ' Untersuchungen ueber nied. Seethiere/ p. 91. 



5 ' Mem. de FAcademie imp. des sc. de St. Petersbourg/ vii e ser., torn, x, No. 3, 1867. 



6 c Zeitsch. f. w. Zool./ Bd. xxi, 3, p. 383. 



