8 THOS. H. MONTGOMERY, 



other species examined. Aud since the same stain may also act 

 differently on different species, and since a stain or fixative may serve 

 for the study of one tissue, and be of no practical value for another, 

 I would insist upon the importance of usiog both various fixatives 

 and various stains, for the finer cytological study. The methods 

 advocated here, are the results of some three months experimen- 

 tation. 



For the clearing of sections, and as a medium of transference 

 from alcohol to paraffine, cedar oil is preferable to clove oil, xylol, 

 benzine or turpentine oil. 



A. The Connective Tissues. 



I. Carinella annulata Montagu. 



The connective tissue elements of this species have been studied 

 to some extent by Hubrecht ('75 a, b, '87) and by Bürger ('90, '95 b). 

 I distinguish the following kinds: 



1) Branched connective tissue cells, with more or 

 less dense intercellular substance. This composes the so- 

 called basement membrane of the external epithelium; the outer and 

 inner neurilemmatic layers; the sheaths around the muscle fibres, and 

 bundles of muscle fibres, in the outer circular, longitudinal and inner 

 circular layers, and in the muscle layers of the proboscis, and its 

 sheath; the layer immediately investing the intestine; the layer out- 

 side of the endothelium of the blood vessels (Burger's, '90, "gallertige 

 Grundschicht"), both in the head and trunk; and perhaps the enve- 

 loping membrane of the gonads. 



The so-called basement membrane („Basalmembran") of the ex- 

 ternal epithelium, is, strictly speaking, not a true epithelial basement 

 membrane, since it is not a product of the epitbehal cells ; but as 

 the previous describers of Nemertean histology have employed this 

 term, I also will use it, in order to avoid confusion. This membrane 

 is on cross- section not of uniform thickness, but thicker portions 

 alternate with thinner (Fig. 1); siuce its substance is denser, and 

 stains more deeply, at the latter portions, the decrease in thickness 

 must be caused by the contraction of its radial fibres ; this fact, even 

 the presence of the radial fibres alone, would show that the mem- 

 brane is pliant and elastic. It is not "skeletogenous" (Bürger, '90), 

 since it produces no skeletal structure, being itself the subepithelial 



