138 REPORT — 1855. 



distinguished by a peculiar form of the seraitendinosus, which is similar to that of 

 mammals. 



The ostrich shows some of the greatest peculiarities in the form of the sternal and 

 clavicular muscles in connexion with the modifications of the bones. There is no 

 femoro-caudalis, tibialis posticus, nor peroneus brevis. The most remarkable pecu- 

 liarity is in the existence of the second bead of the vastus internus, which is like a 

 gracilis muscle, which indeed it has been called. This is also the case in the Casso- 

 wary and Apteryx. In all other birds the gracilis is quite lost. 



The Gallinre have the greatest number of muscles present among birds ; the 

 Podiceps (Natatores) the fewest, wanting the ambiens, femoro-caudal, semimem- 

 branosus, gluteus maximus, flexor arctic, prim, digit, secundi, peroneus brevis, digital 

 tendon of peroneus longus, the femoral head of the semitendinosus, and the gastro- 

 cnemius medius. 



On the Formation and Structttre of the Spermatozoa in Ascaris mystax. 

 By Professor Allen Thomson, M.D., F.R.S. 



This paper contained an account of observations instituted by the author, with 

 the view of ascertaining the validity of the objections raised by Professor Bischoff 

 of Munich to the views of Dr. Henry Nelson on the subject of the fecundation of 

 the ova oi Ascaris mystax, and which were communicated by the author to the 

 Royal Society in 1851. Professor Bischoff considered the bodies described by Dr. 

 Nelson as spermatozoa to be nothing more than peculiar epithelial particles belong- 

 ing to the female passages ; but Professor Thomson has succeeded in showing in 

 full detail the whole progress of development of the peculiar flask-shaped spermatic 

 bodies which Dr. Nelson found in the female Ascaris, from their earliest stages in 

 the male, and has thus proved satisfactorily their spermatic nature. 



The following are the principal steps of the development of these spermatic 

 bodies : — 1st. They arise by cell- germs in the uppermost csecal extremities of the 

 male testicular tubes ; which cell-germs are probably not formed singly, but by 

 endogenous increase within parent-cells. 2nd. In the next part of the tube, which 

 is opake or granular, each of these cell-germs is surrounded by a mass of fine 

 granular matter, so as to constitute each an aggregated cell, at first without any 

 external wall, but afterwards this wall is formed by deposit or change round the 

 granular mass. 3rd. The granular nucleated sperm-cell is divided into four, and 

 the granular matter of each portion assumes a remarkable appearance of radiated 

 lines. These remain united together for a time. 4th. The four cells next separate 

 from each other, the radiated linear appearance returns to the granular state, and 

 each of these cells is the source of a spermatic corpuscle. 5th. In general the sper- 

 matic cells do not advance beyond this stage, so long as they remain within the 

 male organs ; but in some cases the author perceived transitions to the forms that 

 are found in the female passages, and was thus enabled to prove the identity of the 

 two sets of bodies. The formation of the spermatozoon from the last-mentioned 

 cells took place by the clearing up of one part of the outer or granular part, and 

 the removal of the granules to the other side ; while the spermatozoon itself was 

 produced by the thickening of the wall of the nucleus in the shape of a dome or 

 hemisphere on one side of the nucleus, the open side of the dome being occupied 

 by the remains of the granular matter and the nucleolus. 6th. In the female pas- 

 sages, the higher these spermatic cells have ascended, the more advanced are they 

 found in the changes of the nucleus into the spermatic body, until iu the upper part 

 of the oviduct, where they first encounter the ova, and, according to Dr. Nelson, 

 effect fecundation, they have attained their full development, and have assumed the 

 peculiar flask or test-tube shai)e. In the lower parts of the female passage, every 

 stage of transition, from the forms observed in the lower part of the vas deferens of 

 the male, through the dome, bell, flask, and test-tube forms, is to be found. 



The author pointed out the peculiarity of form and mode of development belong- 

 ing to those spermatozoa which, as in the Ascaris, are acaudal and motionless. The 

 highly refracting part of the spermatic cell, which assumes the dome or flask-shape, 

 he regarded as corresponding with the body part of the spermatozoa in the higher 



