26 THOS. H. MONTGOMERY, 



the intima of the blood vessels and rhynchocoelom ; and also a layer 

 on the inner surface of the longitudinal muscle layer, enclosing the 

 gonads and lateral nerve chords (Fig. 33 Mem). 



This tissue may be most easily studied in the basal membrane 

 of the outer epithelium (Fig. 36). There it is composed of a faintly 

 staining (with haematoxylin), structureless intercellular substance, in 

 which a few vacuolar cavities (Vac) are present. In some of these 

 vacuoles lie the multipolar cells, whose irregularly branching fibres 

 form a network in the intercellular substance; the oval or elongate, 

 deeply staining nuclei are centrally situated. Since the long axes of 

 these nuclei are usually parallel to the surface of the basement mem- 

 brane, it is probable that the latter is at an early ontogenetic stage 

 very thin, and increases in size by the successive addition of other 

 thin layers. The nuclei in the basement membrane stain less deeply, 

 than in the other portions of this tissue, and evidences of nuclear 

 degeneration are present; this would imply that the basement mem- 

 brane is a more or less dead, merely supporting tissue in the mature 

 worm. 



Between the muscle fibres this tissue occurs in the form of ir- 

 regular threads, which have the appearence of coalesced cell fibres, the 

 intercellular substance being much reduced in amount. This tissue is 

 much more abundant in the head region. 



As in plainly seen on cross section, this connective tissue forms 

 a sheath separating the intestine from the longitudinal muscle layer 

 (Fig. 33 Mem), this layer dividing so as to enclose the nerve chord, 

 lateral vessels, and gonads — as is apparently the case in all Meta- 

 nemerteans. As is well known, the blood vessel lies beneath the 

 nerve chord, and the gonads above or below it. We have just seen 

 that this connective tissue sheath splits, so as to enclose the organs 

 mentioned, forming two layers on each side, bounding the nerve and 

 blood vessel on both sides; it is, now, the external layer which 

 Salensky ('84) terms the "somatopleure", and the inner layer he 

 terms the "splanchnopleure". But there is no open cleft, nor even 

 a "fente insignifiante", between the two layers, as stated by Salensky, 

 though not apparent in his figures, which would correspond to his 

 "coelome" ; since these layers are coalesced respectively with the outer 

 and inner neurilemma of the nerve chord, and with the connective 

 tissue layer of the blood vessel. And though my own observations 

 on AmpMporus, Tetrastemma and Stichostemma corroborate Salensky's 

 on Monopora, that "c'est le tissu conjonctif qui revêt les cordons 



