ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 701 



are differentiated single cells, viz., muscular fibres or chloragogen cells, 

 whilst almost all the others leave their basal membrane (peritoneal in 

 origin), perhaps to fulfil further functions as lymph-cells of the coelorae. 

 The ventral vessel and side offshoots are represented only by the basal 

 membrane and isolated cells projecting exteriorly. The amcebocytes of 

 the blood are either lymphocytes which have immigrated from the body 

 cavity, or more probably they have arisen from mesenchyme cells which 

 in the embryo have penetrated between the gut and the ccelomic cavities, 

 and then, attaching themselves to the ventral vessel wall, and increasing in 

 numbers, form in some types a heart-body, whose function is that of a 

 valve and also of a secreting gland. 



Epithelial and Connective-Tissue Cells in Hirudo. — E. Holmgren* 

 describes a peculiar relation which exists in Hirudo between the epithe- 

 lial and connective-tissue cells of the oesophagus and cirrus. While the 

 epithelial cells touch each other at the periphery, their main portion is 

 sunk in the connective tissue. P. Blochmannf points out that this has 

 already been noted by him, not only in Hirudo, but also in all the 

 divisions of Platyhelminthes. He objects to Holmgren's use of the 

 term " membranellas," which he applies to the connective-tissue lamellae 

 between the epithelial cells. Holmgren asserts that " the connective- 

 tissue also sends into the interior of the cells delicate thread-like con- 

 tinuations, and that these under certain circumstances can penetrate the 

 whole cell in order to pass to the other side into the pericellular con- 

 nective-tissue." Blochmann considers this an error, and that it is a 

 question of three cells cut on a slant ; of the two upper ones only the 

 peripheral part is seen, and of the under one only the central portion 

 containing the nucleus. 



Nematohelminth.es. 



Chromosomes of Ascaris.J — I). Tretjakoff describes various pheno- 

 mena in Ascaris, such as the bending and union of the chromosome 

 ends, and the oblique splitting of obliquely placed chromosomes, which 

 are not in agreement with Boveri's hypothesis of longitudinal splitting. 

 The formation designated by Boveri as a chromatic element appears in 

 both varieties bivalens and univalent of Ascaris megalocephala, only as 

 the final stage of a series of alterations during which each chromatic rod 

 exhibits a certain independence ; and consequently the maintenance of 

 the idea of the chromatic element is superfluous. 



Gonad Walls in Ascaris megalocephala.§ — Adalbert Domaschko 

 describes the histology of the different regions of the gonads of Ascaris 

 megalocephala. The -epithelium of the whole gonadic tube (except the 

 vagina) is of mesodermal origin, and in spite of the differences in the 

 nature of the cells occurring there, it must be regarded as having been 

 laid down uniformly. The vagina alone is of ectodermal origin. 



i 



* Arch. Mikr. Anat., Bd. G5 (1904) pp. 280-97 (2 pis.). 

 f Anat. Anzeig., xxvi. (1905) pp. 269-71. 

 % Arch. Mikr. Anat, Bd. 65 (1904) pp. 358-82 (1 pi. . 

 § Arb. Zool. Inst. Wien, xv. (1905) pp. 275-80 (2 pis.). 



