ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 201 



small stinging-cells are distinctly transversely striated ; in the case of 

 the larger cells we find that the stalk contains in its centre large oval 

 nuclei, the contractile substance is broken up into 8-12 transversely 

 striated fibrils placed at regular distances from one another ; at the 

 level of the capsule these branch dichotomously, and at the end where 

 the cnidocil is placed we find a large number of fine contractile fibres 

 converging in a regular manner, and at regular distances. 



Now that the connection of muscles with the stinging-cells has 

 been made certain, it is easy to see what is the real nature of the 

 pressure on the wall of the capsule, which has been universally 

 recognized as necessary for the protrusion of the spiral filament. 

 When the network of fibrils contracts there must be a certain pressure 

 on the wall ; where this network is absent, the contraction of the 

 stalk must press the capsule against the tissues which underlie it ; 

 and both causes may act, as in PJiysalia, at the same time. As to 

 the irritability of the muscles it is to be noted that the necessary 

 connection of the muscular stalk with nervous elements has so far 

 been worked out by Chun in Physalia that ganglionic cells have been 

 there observed, and that sensory hairs are always richly developed in 

 the region of the urticating batteries. 



Morphologically, the stinging-cells appear to represent not glands, 

 the secretion of which forms the capsule, but epithelio-muscular 

 cells. 



Development of the Coelenterata.* — In these comparative embry- 

 ological studies E. Metschnikoif considers the formation of the endo- 

 derm in the Geryonida, and the development of the Cunina parasitic 

 in Carmarina. 



In dealing with the former, the author refers to the doubts expressed 

 by Professor Haeckel as to the reality of the delamination method 

 of the formation of the gastrula ; and relates how in Carmarina fungi- 

 formis he was able, at the stage of the formation of thirty-two blasto- 

 meres, to separate the finely granular ectoplasm from the wide-meshed 

 endoplasm; most of the cells were seen to be dividing, and this 

 process of division was best marked in the nuclear spindle. Those 

 that divided radially gave rise to new blastodermal elements, while 

 others which divided tangentially separated the endoderm from the 

 ectoderm. In a second form, Liriope eurybia, the delamination-process 

 was most clearly observed, some of the blastodermal cells grew deep 

 into the cleavage cavity, the nuclei were seen to be dividing ; when 

 the cell protoplasm was constricted the ectoplasm was almost ex- 

 clusively found in the peripheral and the endoplasm in the central 

 segment. This process was succeeded by the formation of a separate 

 endodermal layer and then of a diblastula. 



Dealing with the Cunina parasitic on Carmarina the author 

 examines the accounts of the formation of the gastrula in the Hydro- 

 meduscB ; and in giving a description of his own observations states 

 that the youngest form examined by him formed a small white dot 

 on the margin of the umbrella of Carmarina fungiformis ; under the 



* Zeitschr. f. wiss. Zool., xxxvi. (1861) pp. 433-44 (1 pi.). . 



