. Journal of morphology. by the separation of the first two blastomeres must beof very exceptional occurrence. 4. Spiral-tailed monsters In the fall of 1910, some embryos shipped by express to theUniversity of Wisconsin and reared there in city water, acquired,in about 8 per cent of their number, the abnormality shown infigures 201 and 202. From the condition of the tail in late larvalstages, specimens affected with this malformation may be desig-nated as spiral-tailed monsters. At first this peculiarity seemed JOURNAL OK MORPHOLOGY, VOL. 23, NO. .3 538 BERTRAM G. SMITH merely the persistence
. Journal of morphology. by the separation of the first two blastomeres must beof very exceptional occurrence. 4. Spiral-tailed monsters In the fall of 1910, some embryos shipped by express to theUniversity of Wisconsin and reared there in city water, acquired,in about 8 per cent of their number, the abnormality shown infigures 201 and 202. From the condition of the tail in late larvalstages, specimens affected with this malformation may be desig-nated as spiral-tailed monsters. At first this peculiarity seemed JOURNAL OK MORPHOLOGY, VOL. 23, NO. .3 538 BERTRAM G. SMITH merely the persistence of an embryonic condition; for in eailystages the tail is always strongly flexed and in these particularcases it failed to straighten out. But as development progressedthe tail became twisted into a pronounced spiral. The illustra-tions show the extreme condition; cases occur forming a series in-termediate between this and the normal. In some cases the backis arched or humped. So far as can be judged from surface views,. Jig. 201 Spiral-tailed moiistor of Cryptobranchus allegheniensis at the timeof hatching. Photographed from the living embryo anaesthetized with chlorc-tone. X 3. the entire abnormality seems to ]3e brought about by the con-stricting effect of a band of tissue lying in the ventral median line. As a result of this malformation, the larva is compelled to lieon one side, and can swim only in a grotesque fashion, with back-ward circling movements. Affected larvae take no food, anddie shortly after using up their supply of yolk. An analysis of the water was secured but the subject has notyet been further investigated. Stockard (()(), p. 119) notedthe occurrence of a similar abnormality in Fundulus embryos. EMBRYOLOGY OF (RYPTOBRAXCHUS 539 5. Critical periods in the life history 111 closing this section it remains to note that there are threestages in the hfe history characterized by unusual mortality—natures examinations occur in these stages. These criticalperiods
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Keywords: ., bookcentury1900, bookdecade1, booksubjectphysiology, bookyear1912
