ON A PRORHYNCHID TURBELLARTAN. 633 



structure. It is perforated by innumerable minute openings — 

 the openings of the ducts of the integumentary glands. In 

 the epidermis, which is about "01 mm. in thickness, nuclei, 

 though they doubtless exist, are not to be made out with cer- 

 tainty in any of the series of sections. The rounded clear 

 spaces, the presence of which is so characteristic of the 

 epidermis of the Turbellaria in general, occur abundantly. A 

 distinct, though thin basement membrane {b.) lies below the 

 epidermis. 



All over the surface there occur at fairly wide intervals (on 

 an average 0*5 mm. apart) remarkable unicellular glands (gl.), 

 which for the sake of distinction I will term the superficial 

 integumentary glands. These are pear-shaped when seen in 

 vertical section, but in transverse section often present a 

 stellate appearance, owing to the presence of processes given 

 oflf from the basal part ; the total length, including the duct, 

 is '07 mm. The broad end lies altogether beneath the epidermis 

 and basement membrane, in the zone of ducts, to be presently 

 referred to, while from the narrow end a short duct pierces the 

 integument to open on the surface. The most striking feature 

 of these glands is the enormous relative size of the nucleus, 

 which almost completely fills the cell, so that sometimes only 

 a very thin layer of cytoplasm is distinguishable around it. 

 This cytoplasm, prolonged into the narrow neck of the cell, is 

 of a very finely granular character, without any appearance of 

 reticular or other structure; it has become stained by the 

 eosin in the sections, and the substance of the deeper or basal 

 part of the cell is much more intensely stained than the rest. 



Immediately below the basement membrane is a thin layer 

 of circularly arranged muscular fibres — the outer circular 

 layer (e. c), and in immediate contact internally with this 

 again is a muscular layer of approximately equal thickness in 

 which the fibres run longitudinally, the outer longitudinal 

 layer (e. I.). Between this and the inner layers of muscle is, 

 over all parts of the body, a broad stratum — the zone ofducts 

 — closely packed with the dilated portions of the ducts (dct.) 

 of the deep integumentary glands. These are so closely placed, 



