416 QUARTERLY CHRONICLE OF MICROSCOPICAL SCIENCE. 



Leech or Fluke. — In the same journal Prof. Semper lias 

 some remarks on the crustacean (^enus Leucifer, and on the 

 curious tentacle-bearing- worm Temnocepliala chilensis para- 

 sitic on Thelphusa, and other freshwater Crustacea, usually- 

 classed with the leeches, but which Prof. Semper would 

 place with the Trematoda. 



Development of the simple Ascidians. — The investigation 

 of the development of these animals, which has become so 

 intensely interesting since Kowalewsky's demonstration of 

 its identity in essentials, and even in many details, Avitli 

 that of Amphioxus, and hence of Yertebrata generally, is still 

 being carried on by German and Russian embryologists. 

 Professor Kiipffer, of Kiel, describes, in ' Schultze's Archiv,' 

 part iii, 1872, the development of Molgula microsiiylionica, 

 n. sp., and the nervous system of the larva of Ascidia men- 

 tula. There have been some curiously contradictory state- 

 ments as to whether Molgula develops through a larval form 

 or directly, and Prof. Kupffer clears up the point in dispute 

 between MM. Hancock and Lacaze Duthiers. The observa- 

 tions on the larva of A. mentula are very interesting. The 

 '' spinal cord" of the larva is shown to possess an axial cel- 

 lular substance and cortical fibrillar substances ; also spinal 

 nerves are described passing from it to the muscles, as 

 Huxley and others have described in Appendicularia. The 

 structure of the eye appears to be peculiar, inasmuch as it 

 presents a transition from the invertebrate to the vertebrate 

 type of eye, with a retina developing from the cerebral vesicle. 



Elias Metschnikoff, in ' K. u. S. Zeitschrift,' ord part, 

 187!^, criticises Kowalewsky as to some minor points of in- 

 terpretation relating to the development of the nervous 

 system, and declares that that naturalist in 1866 had over- 

 looked the true nervous system, and " that I am the dis- 

 coverer of the part in question.'^ We know that Metschnikoff 

 is indebted to Kowalewsky for considerable assistance in 

 carrying on work on the Mediterranean fauna {e.g. the 

 material for his memoir on the development of a Nemertean 

 from a Pylidium-larva), and it seems a pity that these two 

 eminent Kussian embryologists should not live at peace with 

 one another — content to excite the envy and criticism of 

 German naturalists. It will be remembered that Metschni- 

 koff had a very unfortunate dispute as to the proprietorship 

 of a " discovery" with Prof. Leuckart, when he was his pupil 

 at Giessen. Metschnikoff denies that the central nervous 

 system in Ph. mammilaris is derived entirely from the outer 

 layer of the embryo. He maintains that cells of the inner 

 layer also take part in its formation, a very curious and in- 



