214 SUMMARY OF CURRENT RESEARCHES RELATING TO 



these, of which there are seven in the first, and three in the second 

 genus follow ; and then succeeds a chapter on Eeproduction, in which 

 the author af&rms his belief that the now well-known Ehombogen 

 and Nematogen forms are " two consecutive phases in the same in- 

 dividual cycle of life." The evidence in favour of this doctrine is, 

 however, of necessity, indirect ; and it is therefore given in detail. 

 The first doubt as to the accuracy of van Beneden's distinction was 

 raised by the discovery of the fact that, in some cases, representatives 

 of only one class were to be seen in a given Cephalopod. Further, it 

 was found that both forms arise from vermiform embryos, which, so 

 far as one can predict, may give rise to either one or the other. 



The rhombogenic mode of reproduction alone gives rise to a 

 plurinucleated axial cell ; the two kinds of embryos produced by 

 diphygenic individuals arise from two distinct kinds of germ-cells, 

 both of which originate, in succession, in the Infusorigen. First, we 

 have those which are destined to form infusoriform embryos ; the 

 remaining cells give rise to vermiform embryos, by multiplication by 

 division. Like preceding observers, Mr. Whitman has failed to detect 

 any fecundation. 



In dealing with the systematic position of the Dicyemidae, the 

 author cites those authorities who regard them as being degraded 

 Worms ; and, discussing the evidence of Julin, states his conviction 

 that that author has demonstrated the existence of a veritable meso- 

 derm ; the two intermediate cells derived from the two poles of the 

 endodermic cell are really mesodermic, and their presence justifies us 

 in asserting that there is a " transient triploblastic stage " in the 

 Dicyemidae. Further evidence in support of the view that these forms 

 should not form the basis of a group of Mesozoa, is to be found in the 

 fact that they are all parasites. " When we find an animal in the form 

 of a simple sac, filled with reproductive elements, secured by position 

 against enemies, supplied with food in abundance, and combining 

 parasitism with immobility, we have strong reasons for believing 

 that the simplicity of its structure is more or less the result of the 

 luxurious conditions of life which it enjoys, even if its development 

 furnishes no positive evidence of degradation." The DicyemidaB 

 would appear, then, to be Platyhelminths degraded by parasitism, 

 but whether descended from Dinophilus, or the Trematoda, further 

 investigations must decide. 



It is of interest to observe that there appears to be a striking 

 correspondence between the age of the host, and the reproductive 

 phenomena of the parasite. Nematogenic individuals are commonly, 

 and sometimes exclusively, the guests of young Cephalopods ; while in 

 older forms of these Molluscs the rhombogenic is the predominant or 

 sole representative. 



Rotifera without Rotary Organs. — The most striking charac- 

 teristic of the Rotifera is the possession of rotary disks ; yet it appears 

 that species exist that have all other characters of the class, but are 

 devoid of vibratile cilia. The first to notice this was Dujardin, who, 

 in 1841, gave the name of Lindia torulosa to his discovery. Gosse, 

 in 1851, described a form {Taphrocampa annulosa) with similar 



