848 SUMMABT OF CURBENT EESEARCHES RELATING TO 



layer of muscles, while hsBmal lacunar spaces are abundantly found in 

 tlie connective substance ; at the lower portion of tbe oesophagus 

 longitudinal muscular fibres are developed. In the stomach both 

 longitudinal and circular muscles are well develojied ; there is a 

 lining epithelium, an internal layer of connective tissue, an outer 

 layer with capillaries, and an investing epithelium. In the intestine 

 we may distinguish two regions, one of a wide and one of a narrow 

 lumen ; the muscular layers are feebly developed, and a layer of fine 

 fibrils is interposed between them and the lining epithelium ; in the 

 upper part of the intestine c^cal structures are to be detected, which 

 are, possibly, the homologues of organs already known in star-fishes. 

 The connective tissue always consists of fibrils with spindle-shaped 

 cells, and of a ground-substance. 



The generative tubes are divisible into two regions ; the two 

 terminal portions (basal and distal) have the same structure, and the 

 latter acts as an efferent duct : between the two is a region in which 

 the tissues are better developed, the separate epithelial cells are fine 

 and filamentoi;s, and not always distinctly separated from one another ; 

 although this outer epithelium is so well develoiDcd, it does not, 

 ciu'iously enough, take any direct share in the formation of the 

 generative products, which arise rather from the lining epithelium of 

 the tube ; the ova appear to be evacuated en masse. 



The dorsal and ventral vessels have the furm of a system of 

 lacunae in the connective tissue, and in these the blood circulates. In 

 all the tissues and lacunae of the Holothurian there are found amcebi- 

 form cells. The muscles have their fibrils arranged in lamellar 

 fashion, like primitive muscular bundles, and they appear to be of 

 epithelial origin. 



Nervous System. — When we come to compare the tojiographical 

 relations of the nervous system in Holothurians and Asterids, we are 

 struck by the great development of connective tissue, and the feebler 

 development of the integumentary epithelium in the former ; the 

 reverse of these relations obtains in the case of the star-fish. In the 

 latter, as is well known, the nervous system appears to be epithelial in 

 position, but in the former apparently, though not morphologically, 

 the nerve-fibres lie more deeply. Owing to the alteration in the 

 position of the nervous system we observe the following differences in 

 the histological structure of the sucker or pedicel. In Cucumaria the 

 investing epithelium is succeeded by the layer of connective tissue, 

 in which is placed the sensory epithelium and its nerve-fibrils ; then 

 come the muscular layer and the lining epithelium. In the star-fish 

 the epithelium and the nervous layer have the feebly developed 

 connective tissue underlying them. 



After describing in detail the characters seen in Holothurians 

 and Asterids, and criticizing the work of previous writers, the author 

 makes some comparisons between the nervous systems of Echinoderms 

 and Coelenterates. 



In star-fishes we recognize four elements in the ectodermal epi- 

 thelium — supporting cells, sensory cells, ganglionic cells, and nerve- 

 fibrils ; the two latter b^ing the more dee^jly lying. The epithelial 



