96 Mr. E. Ray Lankester's Zoological Ohservations 



complete head with its symmetrically arranged scales never 

 grows at the surface of fission, but only a partially formed ill- 

 shapen head with two or four scales. 



In addition to transverse division, Dicyema reproduces by two 

 kinds of internally produced embryos, as pointed out by pre- 

 vious writers. One kind is like the long worm-shaped parent ; 

 the other is oval, and ciliated at one extremity. No one has 

 succeeded in following out what becomes of this latter "infu- 

 sorian-like embryo ;" but the embryos resembling their parents 

 clearly grow up to the reproductive state within their host's 

 kidney, and are to be seen in all stages. 



I have made out, and hope to figure hereafter, the mode of 

 formation of these two kinds of embryos, which differs con- 

 siderably in the two cases. Each originates from a single 

 nucleated cell, which multiplies. Those cells, however, which 

 grow into infusorian embryos are contained at first in an oval 

 capsule or space, twenty or so together, and escape from this 

 capsule to undergo development in the axial tissue. The 

 worm-like embryos, on the contrary, arise from single cells 

 scattered at intervals in the axial parenchyma, which do not 

 at first present any special characters. 



Dicyemce which are developing infusorian embryos do not 

 at the same time develop worm-embryos. No trace of male 

 reproductive organs is to be seen in these organisms. Their 

 structm'e admits of the most complete investigation, on account 

 of their small size and transparency. 



New type of Infusoria. 



Among some eggs of Terehella, associated with other Infu- 

 soria, I found several specimens of an altogether novel type. 

 The general form was oval ; above the mouth projected a small 

 cephalic tubercle ; round this oral extremity was raised up a 

 large collar or ruffle, which continually opened and shut with 

 a slight spiral twist, and caused the locomotion of the animal, 

 whilst at the same time food was brought into the region of 

 the mouth. This membranous vibratile collar or ruffle may be 

 compared to a blended crown of cilia. It forms one of the rare 

 examples of undulating membranes, similar to that of Undulina 

 (parasitic in the frog's blood, 'Quart. Journ. Micr. Sci.' October 

 1871), where, however, the membrane is in the form of a crest, 

 and not of a collar as here. 



There is not a trace of a cilium on any part of this infuso- 

 rian, the whole work being done by the vibrating collar. 



It is obvious that this form cannot be placed in any one of 

 Stein's divisions of ciliate Infusoria, but must stand alone. 



