ANATOMICAL INVESTIGATIONS. 



INTEGUMENT. 



By " integument " I wish to designate the cellular layers as they are found outside 

 the more or less stratified connective tissue, which is known as the basement membrane. 

 The latter is of very varying thickness, and, for reasons to be given subsequently, will be 

 treated in another paragraph. Glandular structures of the integument, whether enclosed 

 within the cellular layers just alluded to, or stretching inwards between the muscles 

 and piercing a secondary basement membrane, hereafter to be described, only by means 

 of their communicating ducts with the exterior, will also be treated of here. 



Commencing with a description of the integument of the Palseonemertea, it will be well 

 to take the more important genus of which representatives are found amongst the Chal- 

 lenger Nemertea, viz., Carinina, as a type. This is all the more desirable as we shall here 

 find the central nervous system still clearly belonging to the integument, its constituents 

 imperceptibly merging into those of the deeper cellular layers of the skin, and also lying 

 outside of the basement membrane. 



The two specimens of Carinina at my disposal revealed the same features with respect 

 to their integument, although in one of them the granular secretion in the glands that 

 form part of it is much more copious. When we leave out of consideration the basement 

 membrane, that can be easily detected in the sections by the uniform and deep red 

 tint it acquires by the staining reagent (picrocarmine), we can roughly distinguish four 

 constituent strata in the integument not in any way separated by sharp boundary lines, 

 but characterised by the presence of difi"erent histological elements which we will now 

 proceed to describe more fully. It will be understood that the absence of fresh material 

 and the scanty supply of spirit specimens has necessarily limited the exact discrimination 

 of these histoloofical elements. 



Of the four strata alluded to, the one adjoining the basement membrane is extremely 

 important, being the seat of those cellular modifications which must be looked upon 

 as the difierentiation of the central nervous system within the domain of the integu- 

 ment. This position — it was already noticed in the description of the species given 



