198 DISCOVERY REPORTS 



can be traced extending spread out irregularly for some long distance beyond the 

 apparent end of the muscle. 



Before discussing the origin of these circular muscles the dorsal longitudinal system 

 may be dealt with briefly. These muscles lie in the pericardial floor which rests against 

 the inner face of the circular muscles (Fig. 2 d) in the same way as the latter are attached 

 to the cuticle through the ectoderm cells. Their number and disposition is dealt with 

 more fully in the section dealing with the blood system. 



I discussed the origin of the circular muscular system in Ostracods in my paper on 

 Doloria and suggested that these muscles are of the type whose development I had 

 studied in other forms such as Chirocephalus and Cypris and had found to be ectodermal. 

 This view has been criticized by Goodrich, one of whose pupils (Needham, 1937, 

 p. 559) has recently attacked my results and those of Dr Manton who likewise found 

 ectodermal muscles in her work on Hemimysis. Needham's observations were based on 

 material (Neomysis) collected by Professor Goodrich and preserved in Bouin. Now 

 Bouin is a notoriously poor fixative for crustacean embryos, and for this reason it would 

 be unwise to put Needham's figures against the beautiful preparations figured by Miss 

 Manton. It must be remembered that Dr Manton only undertook the embryology 

 of Hemimysis after I had found that B. G. Smith's fixative gave results as near perfect 

 as could be. However, apart from this bad technical fault, Needham argues in favour 

 of his view that among those who suggest that ectodermal muscles may occur " . . .there 

 is not good agreement in the evidence from different forms " (p. 503), and even publishes 

 a table to show how Miss Manton's results disagree with my own. Actually, we do not 

 expect agreement. The fact that the extensor muscles of the limbs are ectodermal in 

 Hemimysis according to Dr Manton, and mesodermal in Chirocephalus according to me, 

 does not mean that one of us must be wrong. In the table Needham publishes he 

 records my observation that the sphincter muscle of the maxillary gland of Cypris is 

 ectodermal while it is mesodermal in Chirocephalus. Does he imply, from his table, 

 that I must be wrong in one of these cases? I can see no other reason for publishing it. 



Needham has evidently not seen my views, with which I think Dr Manton would 

 agree, which I published in my report on Doloria. Here I stated (1931, p. 448) that 

 " . . .the Crustacean ectoderm is. . .a supporting tissue of varied potentialities. It may 

 produce a hard external plate or sclerite. It may pass inwards and produce an endoskeletal 

 apodeme. . . ", and so on. It has these potentialities — that is all I maintain. But the fact 

 that it gives rise to muscles in a certain region in one form does not imply that it does 

 so in the same position in all forms. 



The work on Gigantocypris has added to my observations on Doloria and has strength- 

 ened my view that the whole of this circular system of muscles is actually derived from 

 the ectoderm. First, I have been able to study an embryo where the limits of the ecto- 

 derm cells are very clear, and the discovery of chlorazol black has enabled me to study 

 the distribution of the terminal fibrillae of the muscles. 



The embryo, as I have pointed out above, shows that at an early stage the muscle 

 cells are continuous with the ectoderm cells. Then in the adult the striations which 



