128 MR. A. W. WATEES ON TUBUCELLARIA : 



sheath to the operculum (figs. 19, 20, 25). The polypide in the ovicellular 

 zocecia is, as ah'eady stated, very small, and is referred to as the diminutive 

 polypide ; but although it is so small it is in full vigour, staining throughout 

 and showing no signs of histolysis. The ring-canal, and the so-called ganglion, 

 can be distinguished in this small polypide. Fig. 25 shows how it is formed 

 from an ordinary polypide, for in r we still have the remains of the rectum, 

 while part of the digestive tube [dt), namely the cardiac region, stomach, and 

 csecum, is separating into three cysts, or we may call them brown bodies, and 

 other sections show the changes from the ordinary polypide to the diminutive 

 in various stages. Fig. 25 is one of the most instructive sections, for we have 

 the larva {T) in the ovicell and the ovarium immediately below the diminutive 

 polypide ; and this is what we generally find, though in fig. 20 there are no 

 larvse, as they have probably been shed and another ovum will shortly pass 

 into the ovicell. I have preferred to give fig. 20 as a copy of a section 

 rather than to make it at all diagrammatic, though, in the stage figured, it is 

 rather unusual not to find a larva in the ovicell, and a considerable number 

 of sections show that the existence of the diminutive polypide with a larva 

 in the ovicell and the ovarium immediately below it is no exceptional thing, 

 but the general rule. Young ovaria occur in different places, but very 

 frequently they are found in the neighbourhood of the upper lateral rosette- 

 plate with parenchym-threads extending from the wall as in fig. 24. 



In some Ctenostomata small polypides called " auxiliary polypides " * have 

 been described, and these are formed in zooecia which have previously con- 

 tained an ordinary polypide, though now it has disappeared leaving only a 

 brown body. The only function of these " auxiliary polypides " is said to be 

 to eject the larva, and it is only natural to enquire whether the diminutive 

 polypides of Tuhucellaria have a similar function, though there is nothing to 

 suggest this. In the first place, it is not a fresh polypide, but the original 

 one modified ; then, in the second place, it seems as if the object were to get 

 beyond the larva, for it is connected directly with the aperture of the ovicell. 

 Probably we shall not obtain a full explanation until more species or living 

 ones have been examined. If the object is to obtain direct communication 

 with the exterior medium, could the spermatozoa be thus brought to the 

 growing ova of the ovarium ? 



In Adeonella there is a minute polypide at the distal end of the ovicellular 

 zocBcium, and this will be dealt with shortly. The ovicell is rather like a 

 Chinese puzzle, as there is one sac within another, and in tlie interior one the 

 larva is developed. These calcareous species present great difficulties in study, 



* Metschnikof, Bull, de I'Acad. de St. Petersbourg, vol. xv. p. 607, 1871. 



Nitsche, *' Betracht. iiber die EntwickluDgsgesch. uud Morph. der Biy.," Zeit. fiir wiss. 

 Zool. vol. xxii. p. 467, 1871. 



Joliet, "Biy. des Cotes de France," Arch, de Zool. Exp. et Gen. vol. vi. p. 70, pi. 13. 

 figs. 5-9, 1877. 



