428 SUMMARY OF CURRENT RESEARCHES RELATING TO 



to the mode of life of the larva the fore-brain long remains proportion- 

 ately very small. The riidiment of the olfactory organ is primitively 

 single, and not, as stated by Calberla, double. 



The mesoderm gives rise to some of the voluntary mr.scles, the 

 dermis, a large part of the intramuscular connective tissue, part of 

 the peritoneal membrane, from its outer layer ; and from its inner to 

 the greater part of the voluntary muscles, the axial skeleton, the mus- 

 culature and connective tissue of the heart and enteron, and to a large 

 part of the peritoneal membrane ; as well as to the uropoetic system. 

 In this last, which alone we have space to notice, there is considerable 

 agreement with what is seen in the Amphibia, both of which appear to 

 have retained ancestral arrangements, while the higher Selachii have 

 entered on a new line of development. It is important to note that 

 the infundibula of the head-kidney are metameric ; in the very earliest 

 stage after the appearance of the lumen there are two simple ducts, 

 which open into the coelom. This first stage probably corresponds to 

 a condition that has been inherited, and calls to mind the account 

 given by Biitschli of the same organs in the Platyhelminthes. In the 

 second stage, that of the true head-kidney, the first development of 

 the excretory apparatus of the true vertebrate is seen ; the oldest 

 openings are the furthest forward, just as the head is the oldest part 

 of the organism. For a long time the head-kidneys are the sole 

 excreting organs of the larva, and the number of infundibular orifices at 

 the time when it escapes from the egg may be five, but are ordinarily 

 four. 



Origin of Colonial Organisms.* — Dr. A. Wilson considers that 

 (1) the original condition of organisms is " colonial." The universal 

 segmentation of the egg is a proof of this inference, and the develop- 

 ment of new forms by this so-called process, in low forms like 

 Gregarinae, &c , supports this conclusion. (2) The lower we proceed 

 in the scale of being, the more marked is the tendency to form 

 " colonial " organisms. (3) Arrest of development, by causing an 

 organism to cease progressing at a segregated stage, will tend to 

 produce a " compound " and " colonial " constitution. (4) The plant 

 world is " colonial " in its highest types. Plant-development has not 

 proceeded towards any marked increase of " individuality " over the 

 colonial nature of lower forms. A tree is in many resjDects as 

 markedly " colonial " as a Volmx. (5) The highest animals exhibit 

 lingering traces of an originally " colonial " nature in their histolo- 

 gical composition. (6) The tendency of life-development is towards 

 concentration and the conversion of the " colony " into the true 

 " individual." 



It is suggested, by way of final inference, that the theory and 

 idea of an originally " colonial " constitution may explain the exist- 

 ence, in man and higher animals generally, of those tribal and family 

 associations which mark the upper strata of existence. The semi- 

 independent action of many parts of the higher brain, for instance, 



* Lecture at MiC Koyal Institution. Pee Aun. and Mag. Nat. Hist , vii. (1881) 

 lip. 413-16. 



