298 PROCEEDINGS OF THE ACADEMY OF [1887. 



ON THE HISTOLOGY OF SALPA. 

 BY DR. CHAS. 8. DOLLEY. 



In connection with a study of budding in Salpa by Prof. W. K. 

 Brooks, I have undertaken to review the histology of Salpa. 

 Thirty years ago Prof. P. Leuckart ^ in commencing a study of the 

 same animal made the remark; "Seit fiinfzig Jahren sind diese 

 Thiere uuzahlige Male von Zoologen und Anatomen beobachtet 

 worden, and doch ist das Studium derselben immer noch versprech- 

 end und lohnend fiir den Forscher," which is still true: and though 

 it may at first thought seem presumptuous to expect any thing new 

 from an animal which has been repeatedly investigated during the 

 last eighty years, it was deemed best to go over the ground accord- 

 ing to the improved methods of modern histological research. The 

 work was mostly done in the Biological Laboratory of Johns Hop- 

 kins University, and completed in the autumn of 1884 in the 

 Laboratory of the Zoological Institute in Leipzig. 



The specimens used, collected by the United States Fish Commis- 

 sion in Vineyard Sound, Avere preserved in alcohol, and in chromic 

 or picric acids. 



The so-called "Tunica externa^' or cuticle of Saljm is a secretion 

 product of the ectodermal cells of the ''Tunica interna." It is a hy- 

 aline, homogeneous, elastic material, showing at times, especially in 

 young specimens, a faintly laminated appearance. This lamination 

 is absent in the adult forms, where it is destitute of any appearance 

 of strvicture, the clear field being broken only by minute granules, 

 and occasional small stellate or spindle-shaped cell-like bodies scat- 

 tered irregularly through it. These latter are, so far as I have been 

 able to observe, destitute of nuclei, and have no connection with one 

 another. They are probably the remains of cells which have wan- 

 dered from the ectoderm into' the newly formed cuticular secretion. 

 Like the outer mantle of DoUolum and the "Haus" of Appendic- 

 laria,^ it seems probable that this cuticle is from time to time shed 

 and renewed. I assume this from having found in my collection 

 several empty outer mantles, and also numerous specimens in which 



1 Rudolf Leuckart : "Zoologische Untersuchungen." " Zur Entwickel- 

 ungsgeschichte der Tunicaten. Salpen und verwandte." Giessen 1S54. 



* Basilius Uljanin : "Fauna und Flora des Golfes von Neapel." Mono- 

 graphie X. DoUolum. p. 14. Herausgegeben von der Zoologischen Station zu 

 Neapel, 1884. 



