364 PROCEEDINGS OF THE NATIONAL MUSEUM 



Table 1. — Length and maturity in Parathemisto pacifica. 



Males : 



Number examined 

 Percent mature 



165 55 60 63 51 26 26 20 6 7 

 2 21 41 74 90 100 83 100 



tively. Both species are predominately carnivorous, sometimes can- 

 nibalistic, but also ingest some vegetable matter. 



I have examined the midgut contents of a few specimens of P. pacijica. 

 Consisting of minute greenish or brownish particles, much of the ma- 

 terial was unrecognizable, but some fragments of diatoms and crusta- 

 ceans were identified. The crustacean parts included copepod swim- 

 ming legs and mouthparts (one mandible was recognizable), spines of 

 undetermined origin, and crystalline cones from compound eyes. It 

 seems reasonable to conclude that the food habits of P. pacijica are 

 similar to those of P. gaudichaudii and P. libellula. 



Anatomy of digestive tract: The structure of the alimentary 

 canal of P. libellula is considered briefly by Dunbar (1946). He de- 

 scribes an interesting "gastric apparatus" formed of dorsolateral and 

 ventral sheets projecting backward in the midgut, which he compares 

 with the peritrophic membrane of insects and onychophorans. Dun- 

 bar also states that there are no caeca or diverticula of any kind. On 

 this point my findings do not agree with his. 



In P. pacijica a pair of caecae arise laterally from the midgut near 

 its anterior end. They extend posteriorly along the entire length of 

 the pereon and run along in close association with the lateral parts of 

 the midgut and with the gonads which lie dorsal to them. The caecae 

 usually have a coarsely vesicular appearance; in section the vesicles 

 are seen to be large vacuolate cells. The vacuoles are filled with an oily 

 or fatty material, and vary greatly in size. In some individuals the vac- 

 uolate cells are so large that the lumena of the caecae are nearly obliter- 

 ated; in others the vacuoles are small and the lumena well defined. 



Contrary to Dunbar's statement, a pair of caecae is also present in 

 P. libellula. Because they are closely applied to and partially fused 

 with the gut wall, their true nature is not obvious in dissected speci- 

 mens, and if the lumen is sufficiently encroached on by the large 



