100 Miscellaneous. 



tbe muscular epithelium. Schultze regards the threads {cnidocih) 

 of the urticating organs as organs of touch. The study of Lucer- 

 nana has enabled me to extend Schultze's observations : the heads 

 of the tentacles of the animal in question are covered with nemato- 

 cysts (urticating organs). Each nematocyst is placed in a cell, 

 which bears a thread. This cell is produced into a long fibril, which 

 traverses another bipolar or multipolar cell. The fibril in question 

 terminates by a small peduncle, which penetrates into ihe memhrana 

 propria. The multipolar cell may be regarded as a nervous cell. 

 The analogy with the tactile organs of the Arthropoda is complete. 

 Between these tactile organs there are long glandular cells filled 

 with a mucous substance, which enables the Lucernaria to attach 

 itself by its tentacles. 



The digestive cavity contains a stomach and four wide radial 

 canals ; the walls of this cavitj* are clothed with a layer of ento- 

 dermic cells, which are ciliated on the peristome and simple on the 

 outer walls of the body. Among the entodermic elements there 

 are unicellular flask-shaped glands, which secrete a digestive fluid. 

 The surface of the cavity above mentioned is increased by mesen- 

 teric filaments. One side of each filament is formed by glandular 

 cells, whilst the other is ciliated. I suppose that the ciliated cells 

 serve to produce a cii'culation in the cavity, and the simple ento- 

 dermic cells absorb the nutritive liquid. 



The sexual elements are developed in special capsixles of ento- 

 dermic origin. Each capsule is composed of the entoderm and of 

 an elastic membrane (membrana proi^ria) ; the interior of the cap- 

 sule is filled ^^•ith ovigenous cells ; the young ovum has a largo 

 germinal vesicle, which disappears as it enlarges. The developed 

 ovum is surrounded by a strong membrane with a large micropyle. 

 The mature capsule is furnished, near its base, with a duct, which 

 serves for the issue of the sexual products ; this duct is closed, 

 which is due to the elasticity of the memhrana p>ropria. The pres- 

 sure of the mature ova from the interior opens the duct ; a few ova 

 issue, and the duct closes again. — Comptes Mendus, November 8, 

 1875, p. 827. 



Insthict(?) in Hermit Crabs. By Alexander Agassiz. 



While tracing the development of one of our species of hermit 

 crabs I raised from very young stages a number of specimens till they 

 reached the size when they need the protection of a shell for their 

 farther development. I was, of course, curious to see how they 

 would act when first supplied with the necessary shells. For this 

 purpose, a number of shells, some of them empty, others with the 

 animal living, were placed in the glass dish with the young crabs. 

 Scarcely had the shells reached the bottom before the crabs made a 

 rush for the shells, turned them round and round, carefully examin- 

 ing them, invariably at the mouth ; and soon a couple of the crabs 

 decided to venture in. which thev did with remarkable alacrity ; and 



