446 GENERAL HISTORY OF THE INFUSORIA. 



and the young animal creeps out." In a specimen of Brachionus Baker i the 

 first thing Mr. Brightwell detected was a motion like that of the muscular 

 oesophagus of the parent. 



The best account we have of the subject is that given by Prof. Williamson 

 of the Melicerta ringens : — " The first trace," he says, " of futm-e organiza- 

 tion which presents itself, appears in the form of a few freely moving cilia 

 .... at two points, one of which corresponds with the future head, the other 

 near the centre of the ovum .... with the cavity of the stomach ; shortly 

 after .... traces of the central parts of the dental apparatus present them- 

 selves, this, again, being soon succeeded by the union of the entire mass of 

 yolk-cells, and the formation from them of the various organs of the animal. 

 The ciHa now play very freely, especially at the head. The creatm^e twists itself 

 about in its shell ; two red spots appear near the head, which Ehrenberg re- 

 gards as organs of vision, and along with them a very dark-brown and some- 

 what larger spot is developed in the integument near the lower stomach. 

 The young animal now bursts its shell ; . . . . and although its external ap- 

 pendages (XXXYII. 15), and especially the rotatory organs are imperfectly 

 developed or unexpanded, yet the whole of its internal organization, though 

 but obscurely seen, is nevertheless that of the perfect animal, and not that of 

 the larval state." 



In the embryo animal, whilst ^\athin the egg (XXXYII. 2 h), as well as 

 for a short time after its escape (XXXYII. 3, 4 6), Leydig finds in most Eo- 

 tatoria the collection of black or dark-brown particles close upon the cloaca 

 (XXXYIII. 7, 8, 9), which has been described in the section on Secretion, 

 as a supposed mass of urinary concretions. 



The period occupied in the development of the embryo differs in different 

 species. Ehrenberg stated that in Hydathia senta, eleven hours after the 

 deposition of a complete ovum, vibration of the anterior ciha was \isible, and 

 in 24 hours the young being escaped from its shell. Mr. Brightwell, in his 

 notice of Brachionus Baheri, states that ^' about 2 o'clock the animal was ob- 

 served Avith one egg placed externally between the two posterior spines of 

 the shell, and another small egg in the left side of the animal, which increased 

 much in size in the course of the day ; at 9 in the evening a motion was per- 

 ceived in the exterior egg like that of the muscular oesophagus of the parent ; 

 and about this time the internal egg was protruded and placed by the side of 

 the other, being longer than it. At 11 the young BracJiionus burst with a 

 boimd from the egg in which the motion was perceived, and affixed itself by 

 its tail." 



The egg-shell splits open, longitudinally or transversely, to give exit to the 

 young animal. This seems brought about by the active movements of the 

 embryo itself, which sometimes bursts (as Brightwell says) with a bound or 

 spring from its prison. Where the eggs have been attached, the empty fissured 

 shell continues still adherent for a time, until by the movements of the parent, 

 or by some accident, it is detached. 



The variation among different Eotatoria in the stage of development in 

 which the ovum is found when it quits the ovary, or when it is expelled from 

 the body, has been ah-eady remarked ; but additional illustrations are desira- 

 ble. In the greater number, the egg is laid just before or very soon after 

 the process of segmentation of the yelk commences ; for example, in 3feU- 

 certa, Lacinularia, and Brachionus. In many genera the ovum continues in 

 the oviduct, the ovisac, or the cloaca, or otherwise remains within the ovaiy 

 itself until the embryo is complete and even free. Examples of this are found 

 in Stephanoceros, Actinurus, in Rotifer, and in Notommata Syrinx, N. Sie- 

 holdii, and in Asplanclina. In Rotifer, Ehrenberg remarks that, in the ova- 



