178 SUMMARY OF CURRENT RESEARCHES RELATING TO 



outgrowths, which the author explains as due to the advanced state of 

 development of the mesoderm at the time when they originate. 



In Petromyzon the author finds a very simple form of pronephric 

 glomus which hangs ireely in the .body -cavity, and can probably be 

 traced phylogenetically to the pronephric capillary nets of Myxine and 

 the lacunar nets of Amphioxua. As to the Gnathostome glomus, the 

 author is so impressed with the difficulty of hrmologising the primitive 

 retiform glomus with the so-called pronephric glomerulus of Ganoids, 

 Teleosts, and IchthyopMs, that he is disposed to doubt whether the tubules 

 bearing these glomeruli are really pronephric and may not rather be 

 precociously developed mesonephric tubules. 



The author assents to the view that the pronephridia of Vertebrates 

 are homologous with the nephridia of Annelids, and' notices that in Anne- 

 lids, Mollusca, and Insecta there is a tendency for simple larval excretory 

 organs to be replaced by more complex organs, which is analogous to 

 the substitution of mesonephros for pronephros and metanephros for 

 mesonephros in Vertebrates. 



In spite of its length and the number and difficulty of the topics 

 discussed, the paper is without either table of contents or summary. 



Telegony.* — Prof. H. 0. Bumpus gives a brief account of facts and 

 theories of telegony, noting the contribi.tions of A. L. Bell, Pearson, 

 Finn, Bulman, and others, but of Ewart in particular. His conclusion 

 is that " the vexed problems of heredity never will be solved until a 

 great many individuals or institutions seriously undertake experimental 

 breeding." 



b. Histology. 



Cell-Theory.t — Dr. G. Schlater has published a long essay — historical 

 and critical — on the development of the doctrine of the cell. In the 

 first period (Malpighi 1678, Wolff 1759, Mirbel 1809) the cell-wall 

 was known as the boundary of a structural area ; in the second period 

 (Turpin 1826, Schleiden 1838, Schwann 1839) the cell was recognised 

 as a structural unit; in the third period (Leydig 1856, M. Schulze 

 1861) the cell-content of protoplasm rose into greater prominence ; in 

 the modern period (Reinke, Waldeyer) the cell is recognised as an 

 aggregate, a symbiosis, of several independent living substances forming 

 a functional unit. Schlater pleads for a franker recognition of the 

 visible bioblasts (granula, microsomes, cytoblasts), morphological and 

 biological (i.e. structural and functional) units, themselves composed of 

 the invisible vital units, which are built up of albuminoid molecules. 



Structure of Nerve-cells.* — Dr. Emil Holmgren expresses gratifi- 

 cation at the similarity of results obtained by Dr. Studnicka and 

 himself independently from the study of nerve-cells, and describes some 

 further observations of his own on Petromyzon, whose nerve-tissue he 

 had begun to study before the publication of Studnicka's paper. Before 

 doing this, he gives a brief prefatory account of his observations in the 

 case of the higher Vertebrata. He is convinced that the canaliculi, 

 described by himself and Studnicka, do not arise within the cell-body, 



* Amer. Nat., xxxiii. (1899) pp. 917-22. 



t Biol. Centralbl., xix. (1899) pp. 657-81, 689-700, 721-38, 753-70 (2 figs.). 



X Anat. Auzeig., xvii. (1900) pp. 113-29 (17 figs.). Cf. tins Journal, 1899, p. 580. 



