OF THE KOTATORIA. 453 



eighteen days, that duiing this interval it laid four eggs per day, and that 

 the young of these, at two days old, lay a like number. From these data he 

 made an erroneous calculation, that one million individuals may be obtained 

 from one specimen in ten days, that on the eleventh day this brood would 

 amoimt to four millions, and on the twelfth day to sixteen millions. 



This is the only direct observation we have met with intended to prove 

 the remarkable fertility of the class, yet, throughout the history of the 

 Rotifera now detailed, numerous incidental illustrations of the fact occur, — 

 for example, the presence of several ova in different parts of the sexunl 

 apparatus, in various stages of development, and the observed rapidity of the 

 phases of development, at least of summer ova. 



The latter continue to be formed and deposited throughout the whole of 

 the waim part of the year ; and when this di-aws to its close, the production 

 of the winter ova provides for the continuous propagation of the species. 



Ehrenberg, in his specific descriptions, notes the number of ova he met 

 with at the time of obseiwation, intimating that some animals bring forward 

 but one egg at a time, others two or several. 



There is, very probably, a difference in the productiveness of various species ; 

 but differences in this respect will also occur from accidental and external 

 circumstances, such as abundance of food, and changes of temperatiu'e. 



MALE EOTATORIA AJND MALE EEPRODUCTIVE OEGANS. QTJESTIOX OP MALE 

 AjS^D FEMALE ORGANS EST THE SAME INDIVIDUALS. 



Male Rotatoria. — Few male Rotatoria have as yet been determined. Those 

 decisively made out are those of Asplanchna Brightwellii {Notommata anglica, 

 Dalrymple), AsjjlancJina priodonta and A. Boivesii (Gosse), and the Notommata 

 Sieboldii (Leydig). This able German observer argues also that Enteroplea 

 Hydatlna is the male of Hydatina senta, Notoynmata granularis that of N. 

 Brachionus, and Diglena granidaris that of Diglena catellina. Since this was 

 written, Colm has pursued the inquiry, and confirmed Leydig's conjecture, 

 that Enteroplea Hydatina (Ehr.) is the male of Hydatina senta. He has 

 moreover discovered the males of two other species, \dz. of Brachionus urceo- 

 laris and Br. militaris. Still more recently, Leydig has been able to confirm 

 his belief of Enteroplea Hydatina being the male of Hydatina senta (Midler's 

 Archiv, 1857, p. 404) ; and Cohn has discovered the males otEuchlanis dilatata 

 and Notommata Parasitiis (ZeitseJir. 1858, p. 284). Meanwhile Mr. Gosse 

 had discovered the male animals and their eggs in the undermentioned genera 

 and species : — Brachionus Pala, B. ruhens, B. ampliiceros, B. Bakeri, B. angu- 

 laris, B. Dorcas, B. Midleri, Sacculus viridis, Polyarthra platyptera, Synchctta 

 tremida (?), and in all probability MeJicerta ringens, besides the three species 

 of Asplanchna pre^iously detemiined (Phil. Trans. 1856). 



The first male discovered was that of Asplanchna Brightivellii, then sup- 

 posed to be a species of Notommata, and is thus described by Mr. Brightwell 

 (A. N. H. 1848, ii. p. 155) : — It is " about half the size of the female, and 

 differs from it in form, being much shorter and of a rude triangular shape. 

 It is more difficult to detect than the female, being exceedingly transparent, 

 and, from the emptiness of the body, appearing little more than a transparent 

 ciliated bubble. It is very active, and occasionally puffs out the sides of its 

 body, so as entii'ely to alter its form, and remains thus distended some time.'^ 

 There was no indication of any digestive apparatus, or of matters in course 

 of digestion. 



'^ At the bottom of the body, on one side, is a conspicuous round sperm - 

 vessel or testis, in which, under a high power, spermatozoa in active vibra- 

 tile motion may be seen, and at its external side a duct, closed by distinct 



