70 E. LE ROY MICHAEL. 



with the drawings at all. For the general features of the body 

 the camera is necessary, but some measurements are so difficult 

 to discern that one is never quite sure he is tracing correctly. I 

 have found it extremely difficult, in such species as Sagitta en- 

 fiata, to see the cephalic limits of the anterior fin, and have never 

 been able to trace the outline with certainty. I find that an 

 ocular micrometer gives more certain results, with such meas- 

 urements, than the camera. 



Characters Used in Classification. 

 The internal organs of Sagitta consist of the digestive, repro- 

 ductive, and nervous systems. The first includes a simple 

 straight tube leading from the mouth to the anus and offers no 

 definable diagnostic characters ; the two lateral diverticula, used 

 by several writers, would seem to be not real diverticula, but 

 rather results of extreme contraction of the head at death. 

 The size and shape of the vesiculae seminales depend entirely 

 upon the sexual condition of the animal at the time of capture. 

 The extension of the ovaries varies in the different species but, 

 as they are the last organs to develop, one may find an other- 

 wise mature Sagitta with ovaries of any length up to the specific 

 maximum. The shape of the ovaries, whether long and slender, 

 or short and thick, possibly has some significance, but as the 

 length depends largely upon the extent of growth, and the width 

 largely upon the maturity of the ova, too much weight cannot 

 be placed upon these characters. The ova might possibly offer 

 excellent characters for diagnosis, but with our present knowl- 

 edge, one can never be sure whether they are mature or not. 

 The nervous system, if well worked out for every species, might 

 offer excellent characters, but except for two or three species the 

 nervous system has not been investigated. Should the most ex- 

 cellent characters be offered here, their adoption as a means of 

 ready identification would be inconvenient, owing to the technical 

 methods and delicate work required to bring out the points. We 

 are, therefore, compelled to look to the external characters as 

 our only means of accurate identification. 



Even among the external features a few characters have been 

 used in the past, which appear to be worthless for specific deter- 



