38 



SCIENCE. 



[Vol. I., No. 2. 



their observation, there can be no question that there 

 are others which are entirely destitute of them, and 

 have efficient substitutes. Of this character is Dic- 

 tyophora vorax, discovered by Professor Leidy in 

 1857. Tlie animal is oval, transparent, and fixed in 

 its position. Tlie interior exhibits the usual struc- 

 ture of rotifers, tosether with the powerful muscular 

 pharynx armed with jaws, observed to be in frequent 

 motion. From the truncated extremity of the body 

 the auimal projects a capacious delicate membranous 

 cup more than half the size of the body. The cup is 

 a substitute for the rotary disks of ordinary rotifers, 

 and is used as a net to catch food. At will it is en- 

 tirely withdrawn into the body with its prey. The 

 auimal feeds on smaller animalcules; and in one 

 instance upwards of fifty of these, mostly entomostra- 

 cans, were squeezed from the stomach. With ex- 

 tended net, tlie animal measures up to 1 mm. in 

 length. It was found in the Schuyll<ill River, at- 

 tached to stones and aquatic plants, and also was 

 observed attached to the sides of an aquarium. 



MecznilvOW,in 1866, described a similar rotifer under 

 the name of Apsilus lentiformis, found at Giessen, 

 attached to the leaves of the Nymphaea lutea. It es- 

 pecially differs from Dictyophora in the possession 

 of bristled tentacles, and a ganglion to the pouch. 

 Recently, also, Mr. S. A. Forbes of Normal, 111, has 

 described a similar rotifer with the name of Cupelo- 

 pagus bucinedax ; but this Professor Leidy suspects 

 to be the same as the Dictyophora. 



Later Pi-ofessor Leidy has discovered another re- 

 markable form, which he has named, from the ab- 

 sence of rotary organs, and its restless habit, Acyclus 

 inquietus. It was found attached to the stems of 

 Plumatella, a ciliated polyp, on stones in the Schuyl- 

 kill River. It was always single, enclosed in profuse 

 biuiches of the familiar rotifer Megalotrocha, from 

 wliich it was rendered conspicuous by its larger size, 

 resembling a giant in a crowd. For the most part, 

 in general structure it resembles Megalotrocha; but 

 as a substitute for the i-otary disks of the latter, it 

 possesses a large cup-like head prolonged at the 

 mouth into an incurved beak. The cup is retractile 

 and protrusile, contractile and expansile. VVhen 

 protruded and expanded, the mouth gapes widely, 

 and the beak becomes more extended, but always 

 remains incurved. The animal bends incessantly 

 in all directions, and it contracts and elongates in 

 iiccord with its surrounding associates. It frequently 

 bends, almost doublins on itself, so as to bring its 

 prehensile mouth within the play of the currents 

 produced by the rotary disks of the Megalotrochae, 

 while the mouth expands and contracts so as to 

 grasp a portion of the food brought within its reach. 

 Tlie movements of the animal are somewhat of a 

 grotesque character, and reminded the author of 

 a zealous demagogue addressing a crowd, obsequi- 

 ously bowing, and greedily accepting contributions. 

 The lengtli of Acyclus is up to 1..5 mm. in length. 

 The embryo at the time of its escape from the egg is 

 a worm-like body, having the mouth furnished with 

 vibratile cilia. 



The original paper is furnished with illustrations 

 representing both Dictyophora and Acyclus. 



In one instance Professor Leidy remarks, that he 

 had the opportunity of seeing an individual of Plu- 

 matella, with outspread arms, and in its immediate 

 vicinity a group of Megalotrochae with open disks 

 and an Acyclus in its midst, together with two worms 

 of the genus Dero, with extended and expanded 

 branchial tails, all acting together in concert, appar- 

 ently perfectly regardless of the presence of one an- 

 other, — messmates partaking of the same repast. 



RHYTHMIC MUSCULAR CONTRAC- 

 TIONS. 



Continuing those researclies on tire physiology of 

 the contractile tissues to which we owe so much, 

 Engelmann has lately been at work [PfliXfier's arcldv, 

 xxix. 1882) on the arterial bulb of the frog's lieart; 

 selecting it as a muscular organ which contracts 

 rlijthmically on stimulation. Preliminary careful 

 study with tiie aid of some of his pupils confirmed 

 the result of all previous workers, that the bulb con- 

 tains no nerve-cells. LiJwit, however, just as Engel- 

 mann had finished his work, described a 'bulbus 

 ganglion:' this led to a fresh histological examina- 

 tion, also fruitless, so that Engelmann finally asked 

 Lowit to send him some of his preparations. These 

 were received and examined. Engelmann unhesi- 

 tatingly asserts that the supposed nerve-cells are 

 nothing but endothelial elements and connective 

 tissue corpuscles. The isolated arterial bulb is ac- 

 cordingly nothing but a mass of muscular, connec- 

 tive, and epithelial tissues; nevertheless, when filled 

 with blood serum under a suitable pressure, it, like 

 the apex of the ventricle, executes slow rhythmic 

 pulsations. These cease in ten or fifteen minutes, 

 but after a while recommence, and may continue 

 for hours. A single sudden stimulus of ng)derate 

 strength applied in any pause between two pulsations 

 calls forth, not as in the case of the ventricle a single 

 contraction, but a rhythmic series of such. A weaker 

 stimulus leads to only one beat, or none. Any part of 

 the musculature of the bulb has this property, even 

 pieces cut off and so minute as to need a lens for 

 their observ.ition. It is therefore undoubtedly a 

 property of the muscle elements themselves. The 

 muscle is also conductive: a stimulus applied to a 

 portion united only by a narrow uncut strand with 

 another portion, will arouse contractions in the latter. 

 The stronger the stimulus, up to a maximum limit, 

 the greater the number of pulsations in the series 

 which follows its application, and the less the inler- 

 vals between the individual contractions of the series. 

 The influence of successive stimuli at not too short 

 (3-5") intervals is like that observed by Bowditch on 

 the ventricular apex. After long rest, irritability and 

 contractility are diminished; if then equal successive 

 stimuli be applied, of such strength that each only 

 arouses one beat, each beat is more powerful than 

 that which preceded it, until a maximum is reached; 

 at the same time a weaker stimulus than that re- 

 quired at the end of the i^eriod of rest becomes suffi- 

 cient to excite a contraction. Each jDulsation nev- 

 ertheless temporarily exhausts the muscle; if the 

 stimuli follow at loss than 2" intervals, the successive 

 results are smaller. The contraction is always max- 

 imal for the given condition of the muscle: a strong 

 stimulus causes no more powerful contraction than a 

 weak, provided the latter acts at all. As in other 

 muscles, a stimulus in itself too weak to cause a con- 

 traction makes the organ more sensitive to succeed- 

 ing stimuli. As a result of this, rapidly repeated 

 (tetanizing) stimuli at first too feeble to influence the 

 bulb may after a time make it give an occasional beat, 

 and ultimately cause rhythmic pulsations: that is, 

 practically continuous stimulation gives rise not to 

 continuous but to periodic contraction. These exper- 

 iments go far in support of the view which has been 

 gaining ground for some time back, that the rhythm 

 of the heart's action is due not to interraittence in the 

 stimulation sent from its ganglia to its muscle fibres, 

 but to a property of the cardiac muscle tissue itself. 

 The paper also contains interesting experiments on 

 the influence of warmth and cold, and of varied 



