448 GENERAL HISTORY OF THE INFUSORIA. 



Perty seems struck by the considerable variations in form between many 

 embryo and adult Rotatoria, and enunciates the opinion that many supposed 

 perfect forms are no other than embryonic conditions, — for example, GJeno- 

 'phora Trochus, Monocerca vcdga, Notoimnata Felis, and CydogUna elegans. 

 We do not understand whether he believes in a metamorphosis, or if he 

 would simply state that Ehrenberg unnecessarily multiplied genera and spe- 

 cies by describing immatm-e beings as distinct forms. If the latter be all 

 that Perty intends, we entirely concur ^\ith him. 



It is necessary to detail the form and structure of some embryo Rotifera, 

 to illustrate the preceding statements. The embryo of Stephanoceros 

 (XXXVII. 3, 4) is thus described by Leydig : — " It has in general a vermi- 

 cular figui-e. The head, which supports the eyes, is separated from the trunk 

 by a well-marked constriction, and is furnished with long cilia. The head 

 and cilia are retractile. The red specks (two in number) appear actually to 

 be of the natiu'e of eyes ; they have a sharp outline and are slightly concave 

 in front, as if a refracting body was there seated. Within the abdominal 

 cavity behind the head, a peculiar striation is observable, the purpose of 

 which I cannot imagine ; further backward is a clear space in which long 

 cilia are seen in activity, and which indicates the cavity of the alimentary 

 canal. Moreover, the maxillary apparatus, and the special vesicle containing 

 the inorganic particles (uiinary concretions) are perceptible. The termina- 

 tion of the body bears some deKcate vibratile cilia." Beyond this phase of 

 development, the embryo does not advance in the egg, but after being hatched, 

 it would seem to assume another intermediate fomi before arriving at the 

 adult state. Leydig found, in water containing Stephanoceros, a yoimg 

 animal still possessing in some measure the previous vermiform figure and 

 apparent articulation of the trunk and foot, and a proboscis-like head with 

 four projecting arms. The eye-specks were still present. From the trunk- 

 like process of the head, two considerable tubular appendages were out- 

 stretched, ciliated at the extremities : the cilia on the end of the foot-process 

 had disappeared, but were very evident in the abdomen, near to the sac con- 

 taining the inorganic particles. The mandibular apparatus had the regular 

 stmcture. He frequently encountered also another variety, which, together 

 ^dth the figure of the perfect animal, had five arms, but was without any 

 apparent sexual organs, while the foot-process and the w^hole body were 

 strewn with numerous fat-globules. 



We will now continue the description (see p. 446), by Prof. Williamson, of 

 the embrj'o of Melicerta after escaping the egg-shell. He writes — " The 

 young Melicerta stretches itself out, and, everting the anterior part of its 

 body, unfolds several small projecting mammillae covered with large cilia, by 

 means of which it floats freely away (XXXVII. 15, 16). These mammillae 

 are in this stage not unlike those of Notommata clavidata, but they soon en- 

 large and become developed into the flabeUiform wheel organs of the mature 

 animals. The dental apparatus is now fully developed ; the alimentary canal 

 and muscular fasciculi are all present, — only the epithelial cells of the former 

 have not as yet obtained theii' yellow granular contents ; consequently the 

 viscera exhibit the same hyaline aspect as the rest of the organism. The two 

 red specks are imbedded in two of the mammillae. After swimming about 

 for some time like other free Rotifera, the animal imdergoes further changes. 

 The dark-brown spot is the first to disappear ; and soon after, the two pink 

 ones cease to be \asible. The animal attaches itself by the tail to some fixed 

 support, and developes from the skin of the posterior portion of its body a 

 thin hyaline cylinder, the dilated extremity of which is attached to the sup- 

 porting object. The formation of the case is now begim ; the first-formed 



