634 



THE ANIMAL KINGDOM. 



the oviduct. It is rarely ciliated, and always opens dorsally. Both intestine 

 and cloaca are absent in the Asplanchnidae. The mouth, oesophagus, and 

 mastax originate from the stomodaeum ; the cloaca from the proctodaeum ; 

 the stomach, its glands, and the intestine from the archenteron. The 

 nephridia or excretory organs consist of a right and left tube, much con- 

 voluted in places, especially anteriorly. These tubes have nucleated walls 

 and are probably intracellular. They are connected by a transverse canal 

 close behind the ganglion in three or four Rotifers, Lacinularia socialis, 

 Floscularia (sp. ?), Apsilus lentiformis, Hydatina senta. They carry laterally 

 a variable number of ciliated organs, each of which consists of a pyriform 

 canalicule, lodging at its free broad end a flame-cell. The canalicule is 

 closed (Plate), or has a lateral aperture (Eckstein). The two nephridia 

 with a few exceptions end in a contractile vesicle which opens into the 

 cloaca. Except in the Philodinadae the ovarium consists of a germarium 

 and vitellarium (Plate), which are inclosed in a membrane. This membrane 

 is continued into an oviduct which opens into the cloaca. Seison and the 

 Philodinadae have a double, other Rotifera a single, ovarium. 



The male resembles the female in structure in Seison. That of 

 Apodoides stygius does so at first, but with the evolution of the generative 

 organs the alimentary canal becomes reduced to a cellular cord. The male 

 Euchlanis also resembles the female but with the same difference. In all 

 other instances there is a dimorphism. The male is small, with the body 

 pointed posteriorly, a simplified trochal disc, and a soft cuticle. The ali- 

 mentary tract is represented by an irregular cellular cord. The ganglion is 

 unchanged, but the tactile antenna is never stalked. The contractile 

 vesicle of the nephridia may be absent even when present in the female, 

 and then the two vessels have been observed opening on the penis in 

 Hydatina senta : they may unite with the vas deferens. The testis is single, 

 variable in shape ; its duct ciliated, and either ending in an invaginable 

 dorsally placed penis, e. g. Hydatina, Brachionus, &c., or in the posterior 

 pointed termination of the body, e. g. Conochilus. In coitus the penis is 

 inserted at any spot into the coelome, in which the spermatozoa move 

 about freely for a time but after a time perish. The female is therefore 

 parthenogenetic (Plate). The male has not been seen as yet in the Philo- 

 dinadae. 



The ova are of three kinds, small male ova, thin-shelled summer ova, 

 and thick-shelled winter or, better, resting ova ; and a given female lays 

 only one kind (Plate). The ova are sometimes laid and then either float 

 loose or are attached to water-plants or to the mother. The Philodinadae 

 are viviparous, as are some other forms. The ovum then developes in the 

 oviduct or in the coelome, as in Rotifer vulgaris (Zacharias). How the 

 young Rotifer escapes from the parent in this latter case is unknown. 

 There appears to be an epibolic gastrula. 



