35O J. T. PATTERSON. 



are especially common in mammals. For example, my colleague, 

 Dr. C. G. Hartman, has found a great mortality of embryos in 

 the development of the opossum. Degenerating embryos are 

 found throughout the brief but entire period of gestation. 

 Abortive embryos have been found in at least three other species 

 which have a polyembryonic type of development. One of the 

 two embryos which develop from a single egg of the earthworm, 

 Lumbricus trapezoides, sometimes degenerates. Fernandez ('09) 

 has observed rudimentary embryos in the South American 

 armadillo, Tatusia hybrida, and I have on several occasions seen 

 them in the blastocyst of Tatusia novemcincta. But in no case 

 with which we are acquainted is their number and constancy of 

 occurrence so striking as in Copidosoma. 



Our attention was first attracted to these abortive embryos 

 while dissecting out a batch of larvae from a large caterpillar. 

 Most of the larvae in the lot were large and about on the point of 

 undergoing pupation, but in addition to these large individuals, 

 there were a number of smaller ones. At first it was supposed 

 that two distinct species of parasitic larvae were present, or that 

 we had a condition similar to that described by Silvestri for 

 Litomastix, of sexual and asexual larvae. It was noted, however, 

 that the small larvae had the same general structure as the larger 

 individuals, except that they still possessed the two involucres 

 typical of all of the younger larvae of this species. 



A study of serial sections of more than a hundred polygerms 

 has completely demonstrated beyond any possibility of doubt 

 that the small rudimentary embryos are derived from the same 

 egg as larger normal larvae, and consequently do not belong to a 

 different species. The sections show that degenerating embryos 

 are to be found in every stage of development of the polygerm, 

 from the time of the formation of single embryos until the larvae 

 are set free into the body cavity of the host. In Fig. 24 is shown 

 a degenerating embryo which has not yet been completely cut 

 off from its fellow by the constriction of the nucleated membrane. 

 Its nuclei have already completely disintegrated. In Fig. 26 is 

 another embryo well on the way to complete disintegration. 

 Finally Fig. 17, which is a portion of a polygermal mass about at 

 the close of dissociation, contains at least four or five rudimentary 

 embryos. They stain darker than the normal individuals. 



