ZOOLOGY AND BOTANY^ MICROSCOPY, ETC, 59 



digestive tract, the mastax of whieli is incapable of such protrusion as 

 is seen in Notommata ; the author is of opinion that this capacity for 

 protrusion shows that the organ in question is analogous to the armed 

 proboscis of an annelid, and he adds, " nous donnons le nom d'oesophage 

 a la portion suivante du tube digestif," but this is a procedure long 

 since adopted by at least English writers on the anatomy of rotifers. 

 The excretory apparatus is described as being very similar to that of 

 Lacinularia socialis. The contractile vesicle found in most rotifers is 

 absent, and its function seems to be taken on by the spacious cloaca. 

 After some notes on the nervous system, the author passes to the 

 processes of reproduction, to which the largest part of the essay is 

 devoted. 



His more important conclusions may be thus summed up : — 



1. There is no difference in the position of the nervous system 

 and tactile organs of the Melicertidse and other rotifers. As in 

 them, Melicerta has the central nervous system dorsal, that is to say, 

 on the surface which corresponds to the cloacal orifice, and the 

 unpaired tactile organ. Like all rotifers, Melicerta has three tactile 

 organs, an unpaired dorsal, and two lateral pairs. 



2. The organ regarded by Huxley as the ganglion is a gland 

 which is set apart for providing the mucus by means of which the 

 elements of the protective tube are held together. The formation of 

 this tube has been described in a satisfactory manner by Gosse, 

 Bedwell, and Grube. The motile " languette " placed beneath the 

 vibratile pit takes the part of the axis of a wheel. 



3. In the Melicertidae the females may be divided into those which 

 lay male, those that lay summer female, and those that lay winter 

 female eggs. Each appears to have its speciality. 



4. All ova are equally fit for fecundation, but all are not fecun- 

 dated. 



5. The male resembles that of Lacinularia socialis. The sperma- 

 tozoa are ribbon-shaped, have an undulatory movement, and an 

 elongated head. In the body of the female they become immobile, and 

 collect on the surface of the ovary. 



6. Save that perhaps the fecundated egg expels the polar globules, 

 there is no difference in the development of ova coming from a fecun- 

 dated or a virgin female. 



7. The theory of Cohn, according to which only fecundated 

 females lay winter eggs, while the summer ova are developed partheno- 

 genetically, is not in accordance with the facts. 



8. There are reasons for believing that the female fecundated 

 summer egg gives rise to one which lays winter eggs, while a non- 

 fecundated summer egg will only develope into one which lays male 

 or female summer eggs. 



9. There is certainly a relation between the number of males 

 existing at a given time, and the number of winter eggs existing at 

 about the same time. 



10. The winter ought rather to be called durable eggs, for they 

 are destined to resist dryness as much as cold. 



11. The winter have the same early history as the summer eggs, 



