378 DR W. CARMICHAEL M'lNTOSH ON THE STRUCTURE OF THE 



figures do not seem to coincide with each other. He divides the skin into three 

 coats, viz., the ciliated epidermis, cutis, and the fibrous coat. Moreover, the cutis 

 has two layers — an outer, formed of a homogeneous transparent substance, pre- 

 senting in its mass a number of cells or simple rounded vacuoles refracting the 

 light, and an inner, of large elongated cells in a double row ; but in his figure* 

 the muscular elements occupy a bulk so insignificant that some error appears 

 to have been committed, especially as the third layer of the skin is stated to be 

 a transverse fibrous one. It is at all events difficult to see how the enlarged 

 transverse section just noted agrees with his figures iv. and v., pi. 18. Two mus- 

 cular coats only are described by this author — an external longitudinal and an 

 internal circular — the internal longitudinal being omitted, or rather considered as 

 an aponeurotic layer. He also commits a serious error in affirming that the 

 structure of the dermal tissues in Ommatoplea corresponds with that in Borlasia 

 angliw. Frey and Leuckart likewise describe only two muscular coats — an outer 

 longitudinal and an internal circular. Prof. Keferstein,| while representing 

 the cutaneous textures of Cerebratulus (a Borlasian) with greater accuracy, also 

 falls into the mistake of applying what he found in this animal to all the Nemer- 

 teans. He describes the skin as composed of two coats, — a cuticula covered with 

 cilia, and an inner thick, finely granular coat which contains the pigment, — a 

 definition which is scarcely comprehensive enough for the nature of the parts in 

 such as Linens longissimus. He mentions the occurrence of crystals of the form 

 of arragonite in the pigmentary layer of Cephalothrix ocellata, but such have not 

 been seen in the British forms, except under the action of chemicals, or after the 

 evaporation of the salt water. His statement, that in Cerebratulus marginatum 

 there are four muscular coats — an external circular under the pigment-layer of 

 the cutis, a longitudinal, a circular, and lastly an internal longitudinal — has 

 already been noticed. No more than three muscular coats are present in the 

 Borlasians. Lastly, Dr Anton Schneider, in his remarks on the muscles of 

 worms, and their importance in the system,:): states that in Nemertes the follow- 

 ing layers occur : — Circular, longitudinal, and circular, besides radiating muscles 

 — a description that is unsatisfactory as regards the British species. 



Cavity of the Proboscidian Sheath. — This forms a shut sac, as in Ommatoplea, 

 from the bridge of the ganglionic commissure to the posterior end of the worm. 

 The long proboscis glides smoothly in this chamber, whose walls are united with 

 it and other tissues just in front of the commissure. The other contents are the 

 clear proboscidian fluid and its discs. The latter are circular granular bodies, 

 similar to, though smaller than, those of Ommatoplea, and when seen on the 

 edge present a fusiform outline, having a swollen middle and two tapering ends. 

 There are also a few small granules and granular cells. The muscular wall of 



* Op. cit. pi. xxiii, fig. 1. f Op. cit. pp. 66-68. 



t Muller's Archiv fur Anat. 1864, p. 595. 



