NOTES AND MEMORANDA. 421 



abdomen ; in the ScMzopoda and Macrura in the thorax ; in the 

 Galathcidce they extend in front of the digestive stomach, and in most 

 Braclujura they reach to the very anterior portion of the branchial 

 cavity ; the efferent ducts ordinarily open at the coxa of the last pair 

 of thoracic feet. 



II. Structure. In all Becapoda, with the exception of the Pagu- 

 ridce, the testes consist of paired parts and an unpaired piece ; they 

 are generally divided into anterior and posterior lobes, but the unpaired 

 portion varies greatly in position ; in Astacus it is rei)resented by the 

 unpaired hinder lobes, but as a rule it forms one, and in some cases 

 two. connecting pieces set transversely. 



These organs are simplest in structure in Squilla mantis, where they 

 form a tube, the walls of which bulge out into inconsiderable cfeca, 

 which are invested by a sj)erm-producing epithelium ; in Athanas, 

 among the Decapodo, the testes are merely elongated sacs, but the 

 spermigenous epithelium invests regions only of their walls. As the 

 sac elongates, the germinal region becomes broken up, and the testicular 

 tubes attain to an acinous character ; this is seen e. g. in Palcemon, and 

 further stages of complication are observed in Alpheus, in Astacus, 

 and in Homarus. The testes and efferent ducts are always invested 

 by connective tissue, which varies a good deal in character : in Homa- 

 rus it is very well, but in Astacus it is very feebly developed. In 

 various forms, striated muscular fibres were observed in the walls of 

 the testes, the presence of which is explained by the fact that one-half 

 or two-thirds of the testicular tubes here form merely efferent ducts. 



Two sets of elements are distinguished in the germinal elements ; 

 the one set forms large cells with a large rounded nucleus — spermato- 

 blasts ; the other forms a protoplasmic mass in which no cells can be 

 made out, but merely a number of nuclei interposed between the bases of 

 the spermatoblasts ; these nuclei, which vary greatly in form, stain 

 very readily ; these are the reparative germs, so called because they 

 appear to take the place of the effete spermatoblasts ; the difference in 

 these two sets of elements is not to be observed in the young, in which 

 indeed the reparative germs alone appear to be present in any quantity, 

 and what difference there is finally, is shown to be no greater than 

 what obtains in the case of the ovarian cells and the cells of the 

 ovarian follicles ; just as each follicular cell is potentially an ovarian 

 cell, so the reparative germs are potentially spermatoblasts; these 

 latter are formed by the metamorphosis of the reparative germs, just 

 as the ovarian cells are formed from those of the follicle. These con- 

 siderations support the doctrine of the homology of the testis and 

 ovary, as do also the presence of reserve matters in the spermatoblasts, 

 and the striking similarity of the structure of these two organs in such 

 forms as Eupagurus (P. Mayer). 



III. Structure and development of the seminal corpuscles. As 

 is well known, these bodies are markedly distinguished by their 

 "radiate form," but it is pointed out that the equally common belief 

 in their motionless character has certain exceptions ; the simplest 

 arrangement is found in Squilla, in which too their history is most 

 easily followed out ; an elaborate examination leads to the conclusion 



