2 THOS. H. MONTGOMERY, 



My reason for devoting a special study to the connective tissues, 

 is because there has been as yet no satisfactory classification of these 

 tissues in the Nemerteans, and because no comparison of their dif- 

 ferences in representatives of various genera has been made; and 

 such comparative study is necessary, in order to acquire a knowledge 

 of their histogenesis and differentiations, and to enable us to com- 

 pare them with similar tissues in other animal groups. The indis- 

 criminate use of such general terms as "Parenchym", "Connective 

 Tissue", etc. has lead to much confusion, since a careful study shows 

 that a number of morphologically distinct tissues, are thereby grouped 

 together; and in the field of comparative histology, — an important 

 branch of morphology, opened up first by the researches of Leydig 

 and Max Schultze, it is most important to gain an insight into the 

 onto- and phylogenetic relationships of the various connective tissue 

 elements. The recent investigations of v- Graff ('91) and Böhmig 

 ('95 and other papers) have done much to elucidate these tissues in 

 the Turbellaria; but it still remains to carry on such studies, in 

 other groups of the Metazoa, and especially for the Annelida, Mol- 

 lusca and Tunicata. 



In my terminology, I limit the terra "parenchym" to those cells, 

 which are especially characterised by the absence of extracellular fibres, 

 and by the presence of a distinct cell-membrane and of an interr 

 cellular fluid; they have a certain structural resemblance to the 

 parenchym cells of plants. The term "meseuchym" has been applied 

 to those membraneless, usually bipolar cells with branching fibres, 

 which are found in the body cavity, and secrete no intercellular sub- 

 stance; these mesenchym cells retaining the general characteristics of 

 the embryonal mesenchym, to a marked degree. 



Our present knowledge of the connective tissue elements of the 

 Nemerteans is mainly contained in the following papers: 



V. Kennel ('77) has described these tissues in Malacohdella and 

 Geonemertes. In neither did he find a body cavity, filled with a 

 fluid. In Malacohdella, in the young worm (^/^ to 1 mm in length), 

 he found the whole space between the body epithelium und the inner 

 organs, nearly filled with small membraneless cells, with spherical 

 nuclei; these (mesenchym) cells produce the connective tissues, genital 

 cells, and muscle cells of the adult worm. In the latter stage the 

 intercellular gelatinous substance has much increased in amount, and 

 in it lie bipolar, branching cells, and, around the oesophagus, gland 

 cells (sic!). Thus v. Kennel gives a fuller description of the histo- 



