The principles of biology . Fig. 167, we have a species in which thenumber of segments thus united does not exceed four. InEchinohothrium typm there are eight or ten ; and in cestoids THE MOKFHOLOGICAL COMPOSITION OF ANIMALS. 95 generally they are numerous * A considerable hiatus occurs between this phase of integration and the nexthigher phase which we meet with; but it is not greaterthan the hiatus between the tjrpes of the Annuloida and theAnnelida, which present the two phases. Though it isdoubtful whether separation of single segments occurs amongthe Annelida, yet very often we find strin
The principles of biology . Fig. 167, we have a species in which thenumber of segments thus united does not exceed four. InEchinohothrium typm there are eight or ten ; and in cestoids THE MOKFHOLOGICAL COMPOSITION OF ANIMALS. 95 generally they are numerous * A considerable hiatus occurs between this phase of integration and the nexthigher phase which we meet with; but it is not greaterthan the hiatus between the tjrpes of the Annuloida and theAnnelida, which present the two phases. Though it isdoubtful whether separation of single segments occurs amongthe Annelida, yet very often we find strings of segments,arising by repeated longitudinal budding, which after reach-ing certain lengths undergo spontaneous fission: ia somecases doing this so as to form two or more similar stringsof segments constituting independent individuals ; and iaother cases doing it so that the segments spontaneouslyseparated are but a small part of the string. Thus a Syllis,Fig. 168, after reaching a certain length, begins to trans- 0 /66. form itself into two individuals: one of the posterior seg-ments develops into a head, and simultaneously narrows itsconnexion with the preceding segments, from which it * I find that the reasons for regarding the segment of a Tienia as answeringto an individual of the second order of aggregation, are much stronger than I sup-posed when writing the above. Van Beneden says:— Le Proglottis (segment)ayant acquis tout son developpement, se detache ordinairement de la colonic etcontinue encore h. croitre dans Iintestin du memo animal;, il change m6me sou-vent de forme et semble done dune nouveUe vie; ses angles seffacent, tout le corpssarrondit, et il nage comme une Planaire au milieu des muscosites intestinales. 96 MORPHOLOGICAL DEVELOPMENT. eventually separates. Still more remarkable is the extent towhich this process is carried in certain kindred types; whichexhibit to us several individuals thus being simultaneouslyformed out of groups of segments. Fig. 169
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Keywords: ., bookcentury1800, bookdecade1860, booksubjectbiology, bookyear1864
