134 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 1 37 



originate on isps; the other {M. postplenrocoxalis transversus) is a 

 cruciate muscle that originates on lils. This arrangement is essentially 

 what is seen in certain cockroaches, while others appear to have 

 double spinal remotors, isps-cx\, instead (Chadwick, 1957). 



From all these indications, the probability is that the intersegmental 

 coxal remotors of pterygote insects were at one time more diverse than 

 they ordinarily appear to be in those species in which they are pre- 

 served. It is not possible, however, to decide on the basis of present 

 data precisely how the spinal muscles and the cruciate muscles may be 

 interrelated (see section 12, below). 



Another most interesting development is the apparent substitution, 

 in Neuroptera, of a mesosternal remotor of the first coxa for the 

 typical spinal remotor (Korn, 1943; Czihak, 1956; Chadwick, unpub- 

 lished). According to all these authors, the definitive remotor origi- 

 nates near the midline at the junction of the presternum and meso- 

 sternum. Chadwick found that this muscle in adults of an unidentified 

 American species passes ventrolateral to the nerve cord, a significant 

 detail that has now been confirmed for the European forms, both larval 

 and adult, by Czihak (in lit.). Thus, despite the attachment on what 

 has been identified as the spina in larval Myrmcleon (Korn, 1943) 

 and in adult Ascalaphus (Czihak, 1956), the remotor in Neuroptera 

 lacks one of the customary characteristics of all true spinasternal 

 muscles. Yet it seems likely that the muscle in Neuroptera is the 

 homologue of the spinasternal remotor found in other insects, if only 

 because there is no other evident source from which the Neuroptera 

 could have derived it ; and still one must grant that the transfer, in 

 phylogeny or ontogeny, of a muscle attachment across one of the prin- 

 cipal nervous connectives is a most unusual event. If this is what has 

 occurred, we must also consider that what has happened once may 

 happen again, so that we have no guarantee that muscles that are truly 

 spinasternal in one form cannot be homologues of muscles with only 

 paraneural attachments in another. The fact is, of course, that it is 

 the rarity of such shifts that should be emphasized in the present state 

 of our knowledge. 



12. Spinal promotors of the second and third coxa occur in about 

 as many orders as the corresponding remotors, though the pattern of 

 distribution is somewhat different (table i). In Thysanura, the pro- 

 motors also are double (Barlet, 1954, Nos. 106, loy; 112, 11^) ; but 

 they are not so noted in other species, except in the metathorax of 

 larval Dytiscus (Speyer, 1922, No. /// i/). 



Apparent equivalents of the spinal promotors of the mesocoxa were 



