ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 207 



of the tunic) as in most Ascidians ; there are well-developed siphons, 

 and the orifices are widely separated, the dorsal plate is formed by a 

 well-developed continuous membrane, the alimentary canal has a different 

 course to that of Ectcinascidia. The generic characters of the three 

 genera are systematically stated. 



Histology of Salpa.* — Dr. C. S. Dolley has made an investigation 

 into the histology of Salpa. He thinks that the cuticle is, like the outer 

 mantle of Doliolum and the " house " of Appendicularia, shed from time 

 to time, and renewed. The inner mantle is said to consist of an 

 ectodermal and an eudodermal cellular layer, which arc separated by a 

 hyaline connecting substance in which lie buried the viscera and the 

 muscular bands, and through which a network of blood- sinuses burrows 

 in all directions. The ectoderm consists of a single layer of pavement 

 epithelium, in which the cells have the protoplasm occupying the central 

 portion, while the rest of the cell appears to be empty and transparent ; 

 the author has been unable to find large pavement- cells containing a 

 protoplasmic reticulum extending out from a central plasma-mass, as 

 described in the larvso of Doliolum by Uljanin and Grobben ; but in 

 several young specimens he has found a layer of epithelial cells lining 

 the cavity containing the ela3oblast, and these present an appearance 

 which corresponds in almost every particular to that described by Uljanin. 



The muscles are composed of from six to twelve broad, flat, striated 

 fibres arranged in bundles, with their broad surfaces in contact, and their 

 edges looking outwards and inwards. The fibres are made up of several 

 muscle-cells which have become fused together; each fibre has a large 

 number of oval nuclei, which are clear and bladder-like and have 

 relatively large nucleoli. 



The gill is found to be perforated by an irregular series of blood- 

 sinuses, and not by a " single grand sinus " as described by Prof. Huxley. 

 The endostyle of Salpa runcinata-fiisiformis differs considerably from 

 that described by Fol in so many Salpse ; there is no " middle inter- 

 mediary band " ; the " outer intermediary band " does not consist of 

 simple pavement cells, but of three layers of spindle-shaped cells with 

 rod-like nuclei. 



The number of csecal appendages would appear to vary in different 

 species ; the observation of Seeliger that no food is ever found in them 

 is confirmed. Dr. Dolley believes with H. Miiller that they have an 

 hepatic function. The author's objections to the presence of intercellular 

 digestion in Salpa have been confirmed by Seeliger. The existence of 

 cilia for moving on the contents of the intestine is necessitated by the 

 absence of any musculature in connection with the visceral nucleus. The 

 delicate tubes which spread over the visceral network consist of an 

 extremely thin basement membrane, bearing cuboid cells, in which no 

 nucleus was visible. The testes consist of a number of delicate tubes, in 

 which a basement membrane is scarcely apparent ; the walls are formed 

 by a layer of clear round cells containing pear-shaped bodies. 



The nerve-ganglion presents a nearly spherical mass covered with a 

 delicate membrane, which seems to be continuous with the outer sheath 

 of the nerve-trunks. The visual (or as Huxley called it auditory) organ 

 is a continuation both of the central fibrillar core, and the external layer 

 of ganglion-cells ; outside its nervous central portion is a layer of rather 



* Proc. Acad. Nat. Sci. Philad., 1887. pp. 298-308 (1 pi.). 



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